require labels for JUMP opcodes to avoid compiler bugs

Reviewed-on: defunkt/ReefVM#3

CLAUDE.md

@@ -42,8 +42,7 @@ No build step required - Bun runs TypeScript directly.
 - Stack-based execution with program counter (PC)
 - Call stack for function frames
 - Exception handler stack for try/catch/finally
-- Lexical scope chain with parent references
+- Lexical scope chain with parent references (includes native functions)
-- Native function registry for TypeScript interop
 
 **Key subsystems**:
 - **bytecode.ts**: Compiler that converts both string and array formats to executable bytecode. Handles label resolution, constant pool management, and function definition parsing. The `toBytecode()` function accepts either a string (human-readable) or typed array format (programmatic).
@@ -56,7 +55,7 @@ No build step required - Bun runs TypeScript directly.
 
 ### Critical Design Decisions
 
-**Relative jumps**: All JUMP instructions use PC-relative offsets (not absolute addresses), making bytecode position-independent. PUSH_TRY/PUSH_FINALLY use absolute addresses.
+**Label-based jumps**: All JUMP instructions (`JUMP`, `JUMP_IF_FALSE`, `JUMP_IF_TRUE`) require label operands (`.label`), not numeric offsets. Labels are resolved to PC-relative offsets during compilation, making bytecode position-independent. PUSH_TRY/PUSH_FINALLY use absolute addresses and can accept either labels or numeric offsets.
 
 **Truthiness semantics**: Only `null` and `false` are falsy. Unlike JavaScript, `0`, `""`, empty arrays, and empty dicts are truthy.
 
@@ -70,19 +69,22 @@ No build step required - Bun runs TypeScript directly.
 
 **Parameter binding priority**: Named args bind to fixed params first. Unmatched named args go to `@named` dict parameter. Fixed params bind in order: named arg > positional arg > default > null.
 
-**Native function calling**: CALL_NATIVE consumes the entire stack as arguments (different from CALL which pops specific argument counts).
+**Native function calling**: Native functions are stored in scope and called via LOAD + CALL, using the same calling convention as Reef functions. Named arguments are supported by extracting parameter names from the function signature at call time.
 
 ## Testing Strategy
 
 Tests are organized by feature area:
-- **basic.test.ts**: Stack ops, arithmetic, comparisons, variables, control flow
+- **opcodes.test.ts**: Stack ops, arithmetic, comparisons, variables, control flow
 - **functions.test.ts**: Function creation, calls, closures, defaults, variadic, named args
 - **tail-call.test.ts**: Tail call optimization and unbounded recursion
 - **exceptions.test.ts**: Try/catch/finally, exception unwinding, nested handlers
 - **native.test.ts**: Native function interop (sync and async)
+- **functions-parameter.test.ts**: Convenience parameter for passing functions to run() and VM
 - **bytecode.test.ts**: Bytecode string parser, label resolution, constants
 - **programmatic.test.ts**: Array format API, typed tuples, labels, functions
 - **validator.test.ts**: Bytecode validation rules
+- **unicode.test.ts**: Unicode and emoji identifiers
+- **regex.test.ts**: RegExp support
 - **examples.test.ts**: Integration tests for example programs
 
 When adding features:
@@ -135,53 +137,100 @@ Array format features:
 - Function params as string arrays: `["MAKE_FUNCTION", ["x", "y=10"], ".body"]`
 - See `tests/programmatic.test.ts` and `examples/programmatic.ts` for examples
 
-### Native Function Registration
+### Native Function Registration and Global Values
 
-ReefVM supports two ways to register native functions:
+**Option 1**: Pass to `run()` or `VM` constructor (convenience)
+```typescript
+const result = await run(bytecode, {
+  add: (a: number, b: number) => a + b,
+  greet: (name: string) => `Hello, ${name}!`,
+  pi: 3.14159,
+  config: { debug: true, port: 8080 }
+})
 
-**1. Native TypeScript functions (recommended)** - Auto-converts between native TS and ReefVM types:
+// Or with VM constructor
+const vm = new VM(bytecode, { add, greet, pi, config })
+```
+
+**Option 2**: Set values with `vm.set()` (manual)
 ```typescript
 const vm = new VM(bytecode)
 
-// Works with native TypeScript types!
+// Set functions (auto-wrapped to native functions)
-vm.registerFunction('add', (a: number, b: number) => {
+vm.set('add', (a: number, b: number) => a + b)
-  return a + b
-})
 
-// Supports defaults (like NOSE commands)
+// Set any other values (auto-converted to ReefVM Values)
-vm.registerFunction('ls', (path: string, link = false) => {
+vm.set('pi', 3.14159)
-  return link ? `listing ${path} with links` : `listing ${path}`
+vm.set('config', { debug: true, port: 8080 })
-})
-
-// Async functions work too
-vm.registerFunction('fetch', async (url: string) => {
-  const response = await fetch(url)
-  return await response.text()
-})
 
 await vm.run()
 ```
 
-**2. Value-based functions (manual)** - For functions that need direct Value access:
+**Option 3**: Set Value-based functions with `vm.setValueFunction()` (advanced)
+
+For functions that work directly with ReefVM Value types:
+
 ```typescript
 const vm = new VM(bytecode)
 
-vm.registerValueFunction('customOp', (a: Value, b: Value): Value => {
+// Set Value-based function (no wrapping, works directly with Values)
-  // Direct access to Value types
+vm.setValueFunction('customOp', (a: Value, b: Value): Value => {
   return toValue(toNumber(a) + toNumber(b))
 })
 
 await vm.run()
 ```
 
-The auto-wrapping handles:
+Auto-wrapping handles:
-- Converting Value → native types on input (using `fromValue`)
+- Functions: wrapped as native functions with Value ↔ native type conversion
-- Converting native types → Value on output (using `toValue`)
+- Sync and async functions
-- Both sync and async functions
+- Arrays, objects, primitives, null, RegExp
-- Arrays, objects, primitives, and null
+- All values converted via `toValue()`
 
-### Label Usage (Preferred)
+### Calling Functions from TypeScript
-Use labels instead of numeric offsets for readability:
+
+Use `vm.call()` to invoke Reef or native functions from TypeScript:
+
+```typescript
+const bytecode = toBytecode(`
+  MAKE_FUNCTION (x y=10) .add
+  STORE add
+  HALT
+
+  .add:
+    LOAD x
+    LOAD y
+    ADD
+    RETURN
+`)
+
+const vm = new VM(bytecode, {
+  log: (msg: string) => console.log(msg)  // Native function
+})
+await vm.run()
+
+// Call Reef function with positional arguments
+const result1 = await vm.call('add', 5, 3)  // → 8
+
+// Call Reef function with named arguments (pass final object)
+const result2 = await vm.call('add', 5, { y: 20 })  // → 25
+
+// Call Reef function with all named arguments
+const result3 = await vm.call('add', { x: 10, y: 15 })  // → 25
+
+// Call native function
+await vm.call('log', 'Hello!')
+```
+
+**How it works**:
+- Looks up function (Reef or native) in VM scope
+- For Reef functions: converts to callable JavaScript function using `fnFromValue`
+- For native functions: calls directly
+- Automatically converts arguments to ReefVM Values
+- Converts result back to JavaScript types
+
+### Label Usage (Required for JUMP instructions)
+All JUMP instructions must use labels:
 ```
 JUMP .skip
 PUSH 42
@@ -191,6 +240,67 @@ HALT
   HALT
 ```
 
+### Function Definition Patterns
+
+When defining functions, you MUST prevent the PC from falling through into function bodies. Two patterns:
+
+**Pattern 1: JUMP over function bodies (Recommended)**
+```
+MAKE_FUNCTION (params) .body
+STORE function_name
+JUMP .end              ; Skip over function body
+.body:
+  <function code>
+  RETURN
+.end:
+  <continue with program>
+```
+
+**Pattern 2: Function bodies after HALT**
+```
+MAKE_FUNCTION (params) .body
+STORE function_name
+<use the function>
+HALT                   ; Stop before function bodies
+.body:
+  <function code>
+  RETURN
+```
+
+Pattern 1 is required for:
+- Defining multiple functions before using them
+- REPL mode
+- Any case where execution continues after defining a function
+
+Pattern 2 only works if you HALT before reaching function bodies.
+
+### REPL Mode (Incremental Execution)
+
+For building REPLs (like the Shrimp REPL), use `vm.continue()` and `vm.appendBytecode()`:
+
+```typescript
+const vm = new VM(toBytecode([]), natives)
+await vm.run()  // Initialize (empty bytecode)
+
+// User enters: x = 42
+const line1 = compileLine("x = 42")  // No HALT!
+vm.appendBytecode(line1)
+await vm.continue()  // Execute only line 1
+
+// User enters: x + 10
+const line2 = compileLine("x + 10")  // No HALT!
+vm.appendBytecode(line2)
+await vm.continue()  // Execute only line 2, result is 52
+```
+
+**Key points**:
+- `vm.run()` resets PC to 0 (re-executes everything) - use for initial setup only
+- `vm.continue()` resumes from current PC (executes only new bytecode)
+- `vm.appendBytecode(bytecode)` properly handles constant index remapping
+- Don't use HALT in REPL lines - let VM stop naturally
+- Scope and variables persist across all lines
+- Side effects only run once
+
 ## TypeScript Configuration
 
 - Import alias: `#reef` maps to `./src/index.ts`
@@ -376,14 +486,12 @@ Run `bun test` to verify all tests pass before committing.
 
 ## Common Gotchas
 
-**Jump offsets**: JUMP/JUMP_IF_FALSE/JUMP_IF_TRUE use relative offsets from the next instruction (PC + 1). PUSH_TRY/PUSH_FINALLY use absolute instruction indices.
+**Label requirements**: JUMP/JUMP_IF_FALSE/JUMP_IF_TRUE require label operands (`.label`), not numeric offsets. The bytecode compiler resolves labels to PC-relative offsets internally. PUSH_TRY/PUSH_FINALLY can use either labels or absolute instruction indices (`#N`).
 
 **Stack operations**: Most binary operations pop in reverse order (second operand is popped first, then first operand).
 
 **MAKE_ARRAY operand**: Specifies count, not a stack index. `MAKE_ARRAY #3` pops 3 items.
 
-**CALL_NATIVE stack behavior**: Unlike CALL, it consumes all stack values as arguments and clears the stack.
-
 **Finally blocks**: The compiler must generate explicit JUMPs to finally blocks for successful try/catch completion. The VM only auto-jumps to finally on THROW.
 
 **Variable scoping**: STORE updates existing variables in parent scopes or creates in current scope. It does NOT shadow by default.

GUIDE.md

@@ -42,9 +42,6 @@ OPCODE operand     ; comment
 - Booleans: `PUSH true`, `PUSH false`
 - Null: `PUSH null`
 
-**Native function names**: Registered TypeScript functions
-- `CALL_NATIVE print`
-
 ## Array Format
 
 The programmatic array format uses TypeScript tuples for type safety:
@@ -99,11 +96,6 @@ const result = await run(bytecode)
 ["MAKE_DICT", 2]     // Pop 2 key-value pairs
 ```
 
-**Native function names**: Strings for registered functions
-```typescript
-["CALL_NATIVE", "print"]
-```
-
 ### Functions in Array Format
 
 ```typescript
@@ -187,12 +179,25 @@ PUSH 1              ; Named count
 CALL
 ```
 
+**Null triggers defaults**: Pass `null` to use default values:
+```
+; Function: greet(name='Guest', msg='Hello')
+LOAD greet
+PUSH null           ; Use default for 'name'
+PUSH "Hi"           ; Provide 'msg'
+PUSH 2
+PUSH 0
+CALL                ; → "Hi, Guest"
+```
+
 ## Opcodes
 
 ### Stack
 - `PUSH <const>` - Push constant
 - `POP` - Remove top
 - `DUP` - Duplicate top
+- `SWAP` - Swap top two values
+- `TYPE` - Pop value, push its type as string
 
 ### Variables
 - `LOAD <name>` - Push variable value (throws if not found)
@@ -202,6 +207,10 @@ CALL
 ### Arithmetic
 - `ADD`, `SUB`, `MUL`, `DIV`, `MOD` - Binary ops (pop 2, push result)
 
+### Bitwise
+- `BIT_AND`, `BIT_OR`, `BIT_XOR` - Bitwise logical ops (pop 2, push result)
+- `BIT_SHL`, `BIT_SHR`, `BIT_USHR` - Bitwise shift ops (pop 2, push result)
+
 ### Comparison
 - `EQ`, `NEQ`, `LT`, `GT`, `LTE`, `GTE` - Pop 2, push boolean
 
@@ -235,17 +244,54 @@ CALL
 - `DICT_SET` - Pop value, key, dict; mutate dict
 - `DICT_HAS` - Pop key and dict, push boolean
 
+### Unified Access
+- `DOT_GET` - Pop index/key and array/dict, push value (null if missing)
+
+### Strings
+- `STR_CONCAT #N` - Pop N values, convert to strings, concatenate, push result
+
 ### Exceptions
 - `PUSH_TRY .catch` - Register exception handler
 - `PUSH_FINALLY .finally` - Add finally to current handler
 - `POP_TRY` - Remove handler (try succeeded)
 - `THROW` - Throw exception (pops error value)
 
-### Native
-- `CALL_NATIVE <name>` - Call registered TypeScript function (consumes entire stack as args)
-
 ## Compiler Patterns
 
+### Function Definitions
+
+When defining functions, you must prevent the PC from "falling through" into the function body during sequential execution. There are two standard patterns:
+
+**Pattern 1: JUMP over function bodies (Recommended)**
+```
+MAKE_FUNCTION (params) .body
+STORE function_name
+JUMP .end              ; Skip over function body
+.body:
+  <function code>
+  RETURN
+.end:
+  <continue with program>
+```
+
+**Pattern 2: Function bodies after HALT**
+```
+MAKE_FUNCTION (params) .body
+STORE function_name
+<use the function>
+HALT                   ; Stop execution before function bodies
+.body:
+  <function code>
+  RETURN
+```
+
+**Important**: Pattern 2 only works if you HALT before reaching function bodies. Pattern 1 is more flexible and required for:
+- Defining multiple functions before using them
+- REPL mode (incremental execution)
+- Any case where execution continues after defining a function
+
+**Why?** `MAKE_FUNCTION` creates a function value but doesn't jump to the body—it just stores the body's address. Without JUMP or HALT, the PC increments into the function body and executes it as top-level code.
+
 ### If-Else
 ```
 <condition>
@@ -331,6 +377,125 @@ POP
 .end:                    ; Result on stack
 ```
 
+### Reversing Operand Order
+Use SWAP to reverse operand order for non-commutative operations:
+
+```
+; Compute 10 / 2 when values are in reverse order
+PUSH 2
+PUSH 10
+SWAP                     ; Now: [10, 2]
+DIV                      ; 10 / 2 = 5
+```
+
+```
+; Compute "hello" - "world" (subtraction with strings coerced to numbers)
+PUSH "world"
+PUSH "hello"
+SWAP                     ; Now: ["hello", "world"]
+SUB                      ; Result based on operand order
+```
+
+**Common Use Cases**:
+- Division and subtraction when operands are in wrong order
+- String concatenation with specific order
+- Preparing arguments for functions that care about position
+
+### Bitwise Operations
+All bitwise operations work with 32-bit signed integers:
+
+```
+; Bitwise AND (masking)
+PUSH 5
+PUSH 3
+BIT_AND                  ; → 1 (0101 & 0011 = 0001)
+
+; Bitwise OR (combining flags)
+PUSH 5
+PUSH 3
+BIT_OR                   ; → 7 (0101 | 0011 = 0111)
+
+; Bitwise XOR (toggling bits)
+PUSH 5
+PUSH 3
+BIT_XOR                  ; → 6 (0101 ^ 0011 = 0110)
+
+; Left shift (multiply by power of 2)
+PUSH 5
+PUSH 2
+BIT_SHL                  ; → 20 (5 << 2 = 5 * 4)
+
+; Arithmetic right shift (divide by power of 2, preserves sign)
+PUSH 20
+PUSH 2
+BIT_SHR                  ; → 5 (20 >> 2 = 20 / 4)
+
+PUSH -20
+PUSH 2
+BIT_SHR                  ; → -5 (sign preserved)
+
+; Logical right shift (zero-fill)
+PUSH -1
+PUSH 1
+BIT_USHR                 ; → 2147483647 (unsigned shift)
+```
+
+**Common Use Cases**:
+- Flags and bit masks: `flags band MASK` to test, `flags bor FLAG` to set
+- Fast multiplication/division by powers of 2
+- Color manipulation: extract RGB components
+- Low-level bit manipulation for protocols or file formats
+
+### Runtime Type Checking (TYPE)
+Get the type of a value as a string for runtime introspection:
+
+```
+; Basic type check
+PUSH 42
+TYPE                     ; → "number"
+
+PUSH "hello"
+TYPE                     ; → "string"
+
+MAKE_ARRAY #3
+TYPE                     ; → "array"
+```
+
+**Type Guard Pattern** (check type before operation):
+```
+; Safe addition - only add if both are numbers
+LOAD x
+DUP
+TYPE
+PUSH "number"
+EQ
+JUMP_IF_FALSE .not_number
+
+LOAD y
+DUP
+TYPE
+PUSH "number"
+EQ
+JUMP_IF_FALSE .cleanup_not_number
+
+ADD                      ; Safe to add
+JUMP .end
+
+.cleanup_not_number:
+  POP                    ; Remove y
+.not_number:
+  POP                    ; Remove x
+  PUSH null
+.end:
+```
+
+**Common Use Cases**:
+- Type validation before operations
+- Polymorphic functions that handle multiple types
+- Debugging and introspection
+- Dynamic dispatch in DSLs
+- Safe coercion with fallbacks
+
 ### Try-Catch
 ```
 PUSH_TRY .catch
@@ -367,7 +532,8 @@ Functions automatically capture current scope:
 PUSH 0
 STORE counter
 MAKE_FUNCTION () .increment
-RETURN
+STORE increment_fn
+JUMP .main
 
 .increment:
   LOAD counter          ; Captured variable
@@ -376,6 +542,18 @@ RETURN
   STORE counter
   LOAD counter
   RETURN
+
+.main:
+  LOAD increment_fn
+  PUSH 0
+  PUSH 0
+  CALL                  ; Returns 1
+  POP
+  LOAD increment_fn
+  PUSH 0
+  PUSH 0
+  CALL                  ; Returns 2 (counter persists!)
+  HALT
 ```
 
 ### Tail Recursion
@@ -383,7 +561,7 @@ Use TAIL_CALL instead of CALL for last call:
 ```
 MAKE_FUNCTION (n acc) .factorial
 STORE factorial
-<...>
+JUMP .main
 
 .factorial:
   LOAD n
@@ -403,6 +581,15 @@ STORE factorial
   PUSH 2
   PUSH 0
   TAIL_CALL             ; Reuses stack frame
+
+.main:
+  LOAD factorial
+  PUSH 5
+  PUSH 1
+  PUSH 2
+  PUSH 0
+  CALL                  ; factorial(5, 1) = 120
+  HALT
 ```
 
 ### Optional Function Calls (TRY_CALL)
@@ -431,6 +618,96 @@ TRY_CALL unknown       ; Pushes "unknown" as string
 - Shell-like languages where unknown identifiers become strings
 - Templating systems with optional transformers
 
+### String Concatenation
+Build strings from multiple values:
+```
+; Simple concatenation
+PUSH "Hello"
+PUSH " "
+PUSH "World"
+STR_CONCAT #3           ; → "Hello World"
+
+; With variables
+PUSH "Name: "
+LOAD userName
+STR_CONCAT #2           ; → "Name: Alice"
+
+; With expressions and type coercion
+PUSH "Result: "
+PUSH 10
+PUSH 5
+ADD
+STR_CONCAT #2           ; → "Result: 15"
+
+; Template-like interpolation
+PUSH "User "
+LOAD userId
+PUSH " has "
+LOAD count
+PUSH " items"
+STR_CONCAT #5           ; → "User 42 has 3 items"
+```
+
+**Composability**: Results can be concatenated again
+```
+PUSH "Hello"
+PUSH " "
+PUSH "World"
+STR_CONCAT #3
+PUSH "!"
+STR_CONCAT #2           ; → "Hello World!"
+```
+
+### Unified Access (DOT_GET)
+DOT_GET provides a single opcode for accessing both arrays and dicts:
+
+```
+; Array access
+PUSH 10
+PUSH 20
+PUSH 30
+MAKE_ARRAY #3
+PUSH 1
+DOT_GET                 ; → 20
+
+; Dict access
+PUSH 'name'
+PUSH 'Alice'
+MAKE_DICT #1
+PUSH 'name'
+DOT_GET                 ; → 'Alice'
+```
+
+**Chained access**:
+```
+; Access dict['users'][0]['name']
+LOAD dict
+PUSH 'users'
+DOT_GET                 ; Get users array
+PUSH 0
+DOT_GET                 ; Get first user
+PUSH 'name'
+DOT_GET                 ; Get name field
+```
+
+**With variables**:
+```
+LOAD data
+LOAD key                ; Key can be string or number
+DOT_GET                 ; Works for both array and dict
+```
+
+**Null safety**: Returns null for missing keys or out-of-bounds indices
+```
+MAKE_ARRAY #0
+PUSH 0
+DOT_GET                 ; → null (empty array)
+
+MAKE_DICT #0
+PUSH 'key'
+DOT_GET                 ; → null (missing key)
+```
+
 ## Key Concepts
 
 ### Truthiness
@@ -456,6 +733,8 @@ Only `null` and `false` are falsy. Everything else (including `0`, `""`, empty a
 
 **Arithmetic ops** (ADD, SUB, MUL, DIV, MOD) coerce both operands to numbers.
 
+**Bitwise ops** (BIT_AND, BIT_OR, BIT_XOR, BIT_SHL, BIT_SHR, BIT_USHR) coerce both operands to 32-bit signed integers.
+
 **Comparison ops** (LT, GT, LTE, GTE) coerce both operands to numbers.
 
 **Equality ops** (EQ, NEQ) use type-aware comparison with deep equality for arrays/dicts.
@@ -480,11 +759,24 @@ Variable and function parameter names support Unicode and emoji:
 
 ### Parameter Binding Priority
 For function calls, parameters bound in order:
-1. Positional argument (if provided)
+1. Named argument (if provided and matches param name)
-2. Named argument (if provided and matches param name)
+2. Positional argument (if provided)
 3. Default value (if defined)
 4. Null
 
+**Null Triggering Defaults**: Passing `null` as an argument (positional or named) triggers the default value if one exists. This allows callers to explicitly "opt-in" to defaults:
+```
+# Function with defaults: greet(name='Guest', greeting='Hello')
+LOAD greet
+PUSH null    # Triggers default: name='Guest'
+PUSH 'Hi'    # Provided: greeting='Hi'
+PUSH 2
+PUSH 0
+CALL         # Returns "Hi, Guest"
+```
+
+This works for both ReefVM functions and native TypeScript functions. If no default exists, `null` is bound as-is.
+
 ### Exception Handlers
 - PUSH_TRY uses absolute addresses for catch blocks
 - Nested try blocks form a stack
@@ -493,7 +785,7 @@ For function calls, parameters bound in order:
 - Finally execution in all cases is compiler's responsibility, not VM's
 
 ### Calling Convention
-All calls push arguments in order:
+All calls (including native functions) push arguments in order:
 1. Function
 2. Positional args (in order)
 3. Named args (key1, val1, key2, val2, ...)
@@ -501,8 +793,210 @@ All calls push arguments in order:
 5. Named count (as number)
 6. CALL or TAIL_CALL
 
-### CALL_NATIVE Behavior
+Native functions use the same calling convention as Reef functions. They are registered into scope and called via LOAD + CALL.
-Unlike CALL, CALL_NATIVE consumes the **entire stack** as arguments and clears the stack. The native function receives all values that were on the stack at the time of the call.
+
+### Registering Native Functions
+
+Native TypeScript functions are registered into the VM's scope and accessed like regular variables.
+
+**Method 1**: Pass to `run()` or `VM` constructor
+```typescript
+const result = await run(bytecode, {
+  add: (a: number, b: number) => a + b,
+  greet: (name: string) => `Hello, ${name}!`
+})
+
+// Or with VM
+const vm = new VM(bytecode, { add, greet })
+```
+
+**Method 2**: Register after construction
+```typescript
+const vm = new VM(bytecode)
+vm.set('add', (a: number, b: number) => a + b)
+await vm.run()
+```
+
+**Method 3**: Value-based functions (for full control)
+```typescript
+vm.setValueFunction('customOp', (a: Value, b: Value): Value => {
+  return { type: 'number', value: toNumber(a) + toNumber(b) }
+})
+```
+
+**Auto-wrapping**: `vm.set()` automatically converts between native TypeScript types and ReefVM Value types. Both sync and async functions work.
+
+**Usage in bytecode**:
+```
+; Positional arguments
+LOAD add              ; Load native function from scope
+PUSH 5
+PUSH 10
+PUSH 2                ; positionalCount
+PUSH 0                ; namedCount
+CALL                  ; Call like any other function
+
+; Named arguments
+LOAD greet
+PUSH "name"
+PUSH "Alice"
+PUSH "greeting"
+PUSH "Hi"
+PUSH 0                ; positionalCount
+PUSH 2                ; namedCount
+CALL                  ; → "Hi, Alice!"
+```
+
+**Named Arguments**: Native functions support named arguments. Parameter names are extracted from the function signature at call time, and arguments are bound using the same priority as Reef functions (named arg > positional arg > default > null).
+
+**@named Pattern**: Parameters starting with `at` followed by an uppercase letter (e.g., `atOptions`, `atNamed`) collect unmatched named arguments:
+
+```typescript
+// Basic @named - collects all named args
+vm.set('greet', (atNamed: any = {}) => {
+  return `Hello, ${atNamed.name || 'World'}!`
+})
+
+// Mixed positional and @named
+vm.set('configure', (name: string, atOptions: any = {}) => {
+  return {
+    name,
+    debug: atOptions.debug || false,
+    port: atOptions.port || 3000
+  }
+})
+```
+
+Bytecode example:
+```
+; Call with mixed positional and named args
+LOAD configure
+PUSH "myApp"        ; positional arg → name
+PUSH "debug"
+PUSH true
+PUSH "port"
+PUSH 8080
+PUSH 1              ; 1 positional arg
+PUSH 2              ; 2 named args (debug, port)
+CALL                ; atOptions receives {debug: true, port: 8080}
+```
+
+Named arguments that match fixed parameter names are bound to those parameters. Remaining unmatched named arguments are collected into the `atXxx` parameter as a plain JavaScript object.
+
+### Calling Functions from TypeScript
+
+You can call both Reef and native functions from TypeScript using `vm.call()`:
+
+```typescript
+const bytecode = toBytecode(`
+  MAKE_FUNCTION (name greeting="Hello") .greet
+  STORE greet
+  HALT
+
+  .greet:
+    LOAD greeting
+    PUSH " "
+    LOAD name
+    PUSH "!"
+    STR_CONCAT #4
+    RETURN
+`)
+
+const vm = new VM(bytecode, {
+  log: (msg: string) => console.log(msg)  // Native function
+})
+await vm.run()
+
+// Call Reef function with positional arguments
+const result1 = await vm.call('greet', 'Alice')
+// Returns: "Hello Alice!"
+
+// Call Reef function with named arguments (pass as final object)
+const result2 = await vm.call('greet', 'Bob', { greeting: 'Hi' })
+// Returns: "Hi Bob!"
+
+// Call Reef function with only named arguments
+const result3 = await vm.call('greet', { name: 'Carol', greeting: 'Hey' })
+// Returns: "Hey Carol!"
+
+// Call native function
+await vm.call('log', 'Hello from TypeScript!')
+```
+
+**How it works**:
+- `vm.call(functionName, ...args)` looks up the function (Reef or native) in the VM's scope
+- For Reef functions: converts to callable JavaScript function
+- For native functions: calls directly
+- Arguments are automatically converted to ReefVM Values
+- Returns the result (automatically converted back to JavaScript types)
+
+**Named arguments**: Pass a plain object as the final argument to provide named arguments. If the last argument is a non-array object, it's treated as named arguments. All preceding arguments are treated as positional.
+
+**Type conversion**: Arguments and return values are automatically converted between JavaScript types and ReefVM Values:
+- Primitives: `number`, `string`, `boolean`, `null`
+- Arrays: converted recursively
+- Objects: converted to ReefVM dicts
+- Functions: Reef functions are converted to callable JavaScript functions
+
+### REPL Mode (Incremental Compilation)
+
+ReefVM supports incremental bytecode execution for building REPLs. This allows you to execute code line-by-line while preserving scope and avoiding re-execution of side effects.
+
+**The Problem**: By default, `vm.run()` resets the program counter (PC) to 0, re-executing all previous bytecode. This makes it impossible to implement a REPL where each line executes only once.
+
+**The Solution**: Use `vm.continue()` to resume execution from where you left off:
+
+```typescript
+// Line 1: Define variable
+const line1 = toBytecode([
+  ["PUSH", 42],
+  ["STORE", "x"]
+])
+
+const vm = new VM(line1)
+await vm.run()  // Execute first line
+
+// Line 2: Use the variable
+const line2 = toBytecode([
+  ["LOAD", "x"],
+  ["PUSH", 10],
+  ["ADD"]
+])
+
+vm.appendBytecode(line2)  // Append new bytecode with proper constant remapping
+await vm.continue()       // Execute ONLY the new bytecode
+
+// Result: 52 (42 + 10)
+// The first line never re-executed!
+```
+
+**Key methods**:
+- `vm.run()`: Resets PC to 0 and runs from the beginning (normal execution)
+- `vm.continue()`: Continues from current PC (REPL mode)
+- `vm.appendBytecode(bytecode)`: Helper that properly appends bytecode with constant index remapping
+
+**Important**: Don't use `HALT` in REPL mode! The VM naturally stops when it runs out of instructions. Using `HALT` sets `vm.stopped = true`, which prevents `continue()` from resuming.
+
+**Example REPL pattern**:
+```typescript
+const vm = new VM(toBytecode([]), { /* native functions */ })
+
+while (true) {
+  const input = await getUserInput()  // Get next line from user
+  const bytecode = compileLine(input)  // Compile to bytecode (no HALT!)
+
+  vm.appendBytecode(bytecode)  // Append to VM
+  const result = await vm.continue()  // Execute only the new code
+
+  console.log(fromValue(result))  // Show result to user
+}
+```
+
+This pattern ensures:
+- Variables persist between lines
+- Side effects (like `echo` or function calls) only run once
+- Previous bytecode never re-executes
+- Scope accumulates across all lines
 
 ### Empty Stack
 - RETURN with empty stack returns null

IDEAS.md

@@ -0,0 +1,500 @@
+# ReefVM Architectural Improvement Ideas
+
+This document contains architectural ideas for improving ReefVM. These focus on enhancing the VM's capabilities through structural improvements rather than just adding new opcodes.
+
+## 1. Scope Resolution Optimization
+
+**Current Issue**: Variable lookups are O(n) through the scope chain on every `LOAD`. This becomes expensive in deeply nested closures.
+
+**Architectural Solution**: Implement **static scope analysis** with **lexical addressing**:
+
+```typescript
+// Instead of: LOAD x  (runtime scope chain walk)
+// Compile to: LOAD_FAST 2 1  (scope depth 2, slot 1 - O(1) lookup)
+
+class Scope {
+  locals: Map<string, Value>
+  parent?: Scope
+
+  // NEW: Add indexed slots for fast access
+  slots: Value[]  // Direct array access
+  nameToSlot: Map<string, number>  // Compile-time mapping
+}
+```
+
+**Benefits**:
+- O(1) variable access instead of O(n)
+- Critical for hot loops and deeply nested functions
+- Compiler can still fall back to named lookup for dynamic cases
+
+---
+
+## 2. Module System Architecture
+
+**Current Gap**: No way to organize code across multiple files or create reusable libraries.
+
+**Architectural Solution**: Add first-class module support:
+
+```typescript
+// New opcodes: IMPORT, EXPORT, MAKE_MODULE
+// New bytecode structure:
+type Bytecode = {
+  instructions: Instruction[]
+  constants: Constant[]
+  exports?: Map<string, number>  // Exported symbols
+  imports?: Import[]               // Import declarations
+}
+
+type Import = {
+  modulePath: string
+  symbols: string[]  // [] means import all
+  alias?: string
+}
+```
+
+**Pattern**:
+```
+MAKE_MODULE .module_body
+EXPORT add
+EXPORT subtract
+HALT
+
+.module_body:
+  MAKE_FUNCTION (x y) .add_impl
+  RETURN
+```
+
+**Benefits**:
+- Code organization and reusability
+- Circular dependency detection at load time
+- Natural namespace isolation
+- Enables standard library architecture
+
+---
+
+## 3. Source Map Integration
+
+**Current Issue**: Runtime errors show bytecode addresses, not source locations.
+
+**Architectural Solution**: Add source mapping layer:
+
+```typescript
+type Bytecode = {
+  instructions: Instruction[]
+  constants: Constant[]
+  sourceMap?: SourceMap  // NEW
+}
+
+type SourceMap = {
+  file?: string
+  mappings: SourceMapping[]  // Instruction index → source location
+}
+
+type SourceMapping = {
+  instruction: number
+  line: number
+  column: number
+  source?: string  // Original source text
+}
+```
+
+**Benefits**:
+- Meaningful error messages with line/column
+- Debugger can show original source
+- Stack traces map to source code
+- Critical for production debugging
+
+---
+
+## 4. Debugger Hook Architecture
+
+**Current Gap**: No way to pause execution, inspect state, or step through code.
+
+**Architectural Solution**: Add debug event system:
+
+```typescript
+class VM {
+  debugger?: Debugger
+
+  async execute(instruction: Instruction) {
+    // Before execution
+    await this.debugger?.onInstruction(this.pc, instruction, this)
+
+    // Execute
+    switch (instruction.op) { ... }
+
+    // After execution
+    await this.debugger?.afterInstruction(this.pc, this)
+  }
+}
+
+interface Debugger {
+  breakpoints: Set<number>
+  onInstruction(pc: number, instruction: Instruction, vm: VM): Promise<void>
+  afterInstruction(pc: number, vm: VM): Promise<void>
+  onCall(fn: Value, args: Value[]): Promise<void>
+  onReturn(value: Value): Promise<void>
+  onException(error: Value): Promise<void>
+}
+```
+
+**Benefits**:
+- Step-through debugging
+- Breakpoints at any instruction
+- State inspection at any point
+- Non-invasive (no bytecode modification)
+- Can build IDE integrations
+
+---
+
+## 5. Bytecode Optimization Pass Framework
+
+**Current Gap**: Bytecode is emitted directly, no optimization.
+
+**Architectural Solution**: Add optimization pipeline:
+
+```typescript
+type Optimizer = (bytecode: Bytecode) => Bytecode
+
+// Framework for composable optimization passes
+class BytecodeOptimizer {
+  passes: Optimizer[] = []
+
+  add(pass: Optimizer): this {
+    this.passes.push(pass)
+    return this
+  }
+
+  optimize(bytecode: Bytecode): Bytecode {
+    return this.passes.reduce((bc, pass) => pass(bc), bytecode)
+  }
+}
+
+// Example passes:
+const optimizer = new BytecodeOptimizer()
+  .add(constantFolding)      // PUSH 2; PUSH 3; ADD → PUSH 5
+  .add(deadCodeElimination)  // Remove unreachable code after HALT/RETURN
+  .add(jumpChaining)         // JUMP .a → .a: JUMP .b → JUMP .b directly
+  .add(peepholeOptimization) // DUP; POP → (nothing)
+```
+
+**Benefits**:
+- Faster execution without changing compiler
+- Can add passes without modifying VM
+- Composable and testable
+- Enables aggressive optimizations (inlining, constant folding, etc.)
+
+---
+
+## 6. Value Memory Management Architecture
+
+**Current Issue**: No tracking of memory usage, no GC hooks, unbounded growth.
+
+**Architectural Solution**: Add memory management layer:
+
+```typescript
+class MemoryManager {
+  allocatedBytes: number = 0
+  maxBytes?: number
+
+  allocateValue(value: Value): Value {
+    const size = this.sizeOf(value)
+    if (this.maxBytes && this.allocatedBytes + size > this.maxBytes) {
+      throw new Error('Out of memory')
+    }
+    this.allocatedBytes += size
+    return value
+  }
+
+  sizeOf(value: Value): number {
+    // Estimate memory footprint
+  }
+
+  // Hook for custom GC
+  gc?: () => void
+}
+
+class VM {
+  memory: MemoryManager
+
+  // All value-creating operations check memory
+  push(value: Value) {
+    this.memory.allocateValue(value)
+    this.stack.push(value)
+  }
+}
+```
+
+**Benefits**:
+- Memory limits for sandboxing
+- Memory profiling
+- Custom GC strategies
+- Prevents runaway memory usage
+
+---
+
+## 7. Instruction Profiler Architecture
+
+**Current Gap**: No way to identify performance bottlenecks in bytecode.
+
+**Architectural Solution**: Add instrumentation layer:
+
+```typescript
+class Profiler {
+  instructionCounts: Map<number, number> = new Map()
+  instructionTime: Map<number, number> = new Map()
+  hotFunctions: Map<number, FunctionProfile> = new Map()
+
+  recordInstruction(pc: number, duration: number) {
+    this.instructionCounts.set(pc, (this.instructionCounts.get(pc) || 0) + 1)
+    this.instructionTime.set(pc, (this.instructionTime.get(pc) || 0) + duration)
+  }
+
+  getHotSpots(): HotSpot[] {
+    // Identify most-executed instructions
+  }
+
+  generateReport(): ProfileReport {
+    // Human-readable performance report
+  }
+}
+
+class VM {
+  profiler?: Profiler
+
+  async execute(instruction: Instruction) {
+    const start = performance.now()
+    // ... execute ...
+    const duration = performance.now() - start
+    this.profiler?.recordInstruction(this.pc, duration)
+  }
+}
+```
+
+**Benefits**:
+- Identify hot loops and functions
+- Guide optimization efforts
+- Measure impact of changes
+- Can feed into JIT compiler (future)
+
+---
+
+## 8. Standard Library Plugin Architecture
+
+**Current Issue**: Native functions registered manually, no standard library structure.
+
+**Architectural Solution**: Module-based native libraries:
+
+```typescript
+interface NativeModule {
+  name: string
+  exports: Record<string, any>
+  init?(vm: VM): void
+}
+
+class VM {
+  modules: Map<string, NativeModule> = new Map()
+
+  registerModule(module: NativeModule) {
+    this.modules.set(module.name, module)
+    module.init?.(this)
+
+    // Auto-register exports to global scope
+    for (const [name, value] of Object.entries(module.exports)) {
+      this.set(name, value)
+    }
+  }
+
+  loadModule(name: string): NativeModule {
+    return this.modules.get(name) || throw new Error(`Module ${name} not found`)
+  }
+}
+
+// Example usage:
+const mathModule: NativeModule = {
+  name: 'math',
+  exports: {
+    sin: Math.sin,
+    cos: Math.cos,
+    sqrt: Math.sqrt,
+    PI: Math.PI
+  }
+}
+
+vm.registerModule(mathModule)
+```
+
+**Benefits**:
+- Organized standard library
+- Lazy loading of modules
+- Third-party plugin system
+- Clear namespace boundaries
+
+---
+
+## 9. Streaming Bytecode Execution
+
+**Current Limitation**: Must load entire bytecode before execution.
+
+**Architectural Solution**: Incremental bytecode loading:
+
+```typescript
+class StreamingBytecode {
+  chunks: BytecodeChunk[] = []
+
+  append(chunk: BytecodeChunk) {
+    // Remap addresses, merge constants
+    this.chunks.push(chunk)
+  }
+
+  getInstruction(pc: number): Instruction | undefined {
+    // Resolve across chunks
+  }
+}
+
+class VM {
+  async runStreaming(stream: ReadableStream<BytecodeChunk>) {
+    for await (const chunk of stream) {
+      this.bytecode.append(chunk)
+      await this.continue()  // Execute new chunk
+    }
+  }
+}
+```
+
+**Benefits**:
+- Execute before full load (faster startup)
+- Network streaming of bytecode
+- Incremental compilation
+- Better REPL experience
+
+---
+
+## 10. Type Annotation System (Optional Runtime Types)
+
+**Current Gap**: All values dynamically typed, no way to enforce types.
+
+**Architectural Solution**: Optional type metadata:
+
+```typescript
+type TypedValue = Value & {
+  typeAnnotation?: TypeAnnotation
+}
+
+type TypeAnnotation =
+  | { kind: 'number' }
+  | { kind: 'string' }
+  | { kind: 'array', elementType?: TypeAnnotation }
+  | { kind: 'dict', valueType?: TypeAnnotation }
+  | { kind: 'function', params: TypeAnnotation[], return: TypeAnnotation }
+
+// New opcodes: TYPE_CHECK, TYPE_ASSERT
+// Functions can declare parameter types:
+MAKE_FUNCTION (x:number y:string) .body
+```
+
+**Benefits**:
+- Catch type errors earlier
+- Self-documenting code
+- Enables static analysis tools
+- Optional (doesn't break existing code)
+- Can enable optimizations (known number type → skip toNumber())
+
+---
+
+## 11. VM State Serialization
+
+**Current Gap**: Can't save/restore VM execution state.
+
+**Architectural Solution**: Serializable VM state:
+
+```typescript
+class VM {
+  serialize(): SerializedState {
+    return {
+      instructions: this.instructions,
+      constants: this.constants,
+      pc: this.pc,
+      stack: this.stack.map(serializeValue),
+      callStack: this.callStack.map(serializeFrame),
+      scope: serializeScope(this.scope),
+      handlers: this.handlers
+    }
+  }
+
+  static deserialize(state: SerializedState): VM {
+    const vm = new VM(/* ... */)
+    vm.restore(state)
+    return vm
+  }
+}
+```
+
+**Benefits**:
+- Save/restore execution state
+- Distributed computing (send state to workers)
+- Crash recovery
+- Time-travel debugging
+- Checkpoint/restart
+
+---
+
+## 12. Async Iterator Support
+
+**Current Gap**: Iterators work via break, but no async iteration.
+
+**Architectural Solution**: First-class async iteration:
+
+```typescript
+// New value type:
+type Value = ... | { type: 'async_iterator', value: AsyncIterableIterator<Value> }
+
+// New opcodes: MAKE_ASYNC_ITERATOR, AWAIT_NEXT, YIELD_ASYNC
+
+// Pattern:
+for_await (item in asyncIterable) {
+  // Compiles to AWAIT_NEXT loop
+}
+```
+
+**Benefits**:
+- Stream processing
+- Async I/O without blocking
+- Natural async patterns
+- Matches JavaScript async iterators
+
+---
+
+## Priority Recommendations
+
+### Tier 1 (Highest Impact):
+1. **Source Map Integration** - Critical for usability
+2. **Module System** - Essential for scaling beyond toy programs
+3. **Scope Resolution Optimization** - Performance multiplier
+
+### Tier 2 (High Value):
+4. **Debugger Hook Architecture** - Developer experience game-changer
+5. **Standard Library Plugin Architecture** - Enables ecosystem
+6. **Bytecode Optimization Framework** - Performance without complexity
+
+### Tier 3 (Nice to Have):
+7. **Instruction Profiler** - Guides future optimization
+8. **Memory Management** - Important for production use
+9. **VM State Serialization** - Enables advanced use cases
+
+### Tier 4 (Future/Experimental):
+10. **Type Annotations** - Optional, doesn't break existing code
+11. **Streaming Bytecode** - Mostly useful for large programs
+12. **Async Iterators** - Specialized use case
+
+---
+
+## Design Principles
+
+These improvements focus on:
+- **Performance** (scope optimization, bytecode optimization)
+- **Developer Experience** (source maps, debugger, profiler)
+- **Scalability** (modules, standard library architecture)
+- **Production Readiness** (memory management, serialization)
+
+All ideas maintain ReefVM's core design philosophy of simplicity, orthogonality, and explicit behavior.

README.md

@@ -44,10 +44,14 @@ Commands: `clear`, `reset`, `exit`.
 - Variadic functions with positional rest parameters (`...rest`)
 - Named arguments (named) that collect unmatched named args into a dict (`@named`)
 - Mixed positional and named arguments with proper priority binding
+- Default parameter values with null-triggering: passing `null` explicitly uses the default value
 - Tail call optimization with unbounded recursion (10,000+ iterations without stack overflow)
 - Exception handling (PUSH_TRY, PUSH_FINALLY, POP_TRY, THROW) with nested try/finally blocks and call stack unwinding
-- Native function interop (CALL_NATIVE) with sync and async functions
+- Native function interop with auto-wrapping for native TypeScript types
-- Write native functions with regular TypeScript types instead of Shrimp's internal Value types
+- Native functions stored in scope, called via LOAD + CALL
+- Native functions support `atXxx` parameters (e.g., `atOptions`) to collect unmatched named args
+- Pass functions directly to `run(bytecode, { fnName: fn })` or `new VM(bytecode, { fnName: fn })`
+- Call Reef functions from TypeScript with `vm.call(name, ...args)` with automatic type conversion
 
 ## Design Decisions
 
@@ -56,4 +60,5 @@ Commands: `clear`, `reset`, `exit`.
 - Short-circuiting via compiler: No AND/OR opcodes—compilers use JUMP patterns for proper short-circuit evaluation
 - Variadic parameters: Functions can collect remaining positional arguments into an array using `...rest` syntax
 - Named parameters: Functions can collect unmatched named arguments into a dict using `@named` syntax
-- Argument binding priority: Named args bind to regular params first, with unmatched ones going to `@named`
+- Argument binding priority: Named args bind to regular params first, with unmatched ones going to `@named`
+- Null triggers defaults: Passing `null` to a parameter with a default value explicitly uses that default (applies to both ReefVM and native functions)

SPEC.md

@@ -13,10 +13,9 @@ The ReefVM is a stack-based bytecode virtual machine designed for the Shrimp pro
 - **Value Stack**: Operand stack for computation
 - **Call Stack**: Call frames for function invocations
 - **Exception Handlers**: Stack of try/catch handlers
-- **Scope Chain**: Linked scopes for lexical variable resolution
+- **Scope Chain**: Linked scopes for lexical variable resolution (includes native functions)
 - **Program Counter (PC)**: Current instruction index
 - **Constants Pool**: Immutable values and function metadata
-- **Native Function Registry**: External functions callable from Shrimp
 
 ### Execution Model
 
@@ -40,6 +39,7 @@ type Value =
   | { type: 'dict', value: Map<string, Value> }
   | { type: 'function', params: string[], defaults: Record<string, number>,
       body: number, parentScope: Scope, variadic: boolean, named: boolean }
+  | { type: 'native', fn: NativeFunction, value: '<function>' }
 ```
 
 ### Type Coercion
@@ -138,6 +138,24 @@ type ExceptionHandler = {
 **Effect**: Duplicate top of stack
 **Stack**: [value] → [value, value]
 
+#### SWAP
+**Operand**: None
+**Effect**: Swap the top two values on the stack
+**Stack**: [value1, value2] → [value2, value1]
+
+#### TYPE
+**Operand**: None
+**Effect**: Pop value from stack, push its type as a string
+**Stack**: [value] → [typeString]
+
+Returns the type of a value as a string. 
+
+**Example**:
+```
+PUSH 42
+TYPE              ; Pushes "number"
+```
+
 ### Variable Operations
 
 #### LOAD
@@ -179,7 +197,29 @@ All arithmetic operations pop two values, perform operation, push result as numb
 
 #### ADD
 **Stack**: [a, b] → [a + b]
-**Note**: Only for numbers (use separate string concat if needed)
+
+Performs different operations depending on operand types:
+- If either operand is a string, converts both to strings and concatenates
+- Else if both operands are arrays, concatenates the arrays
+- Else if both operands are dicts, merges them (b's keys overwrite a's keys on conflict)
+- Else if both operands are numbers, performs numeric addition
+- Otherwise, throws an error
+
+**Examples**:
+- `5 + 3` → `8` (numeric addition)
+- `"hello" + " world"` → `"hello world"` (string concatenation)
+- `"count: " + 42` → `"count: 42"` (string concatenation)
+- `100 + " items"` → `"100 items"` (string concatenation)
+- `[1, 2, 3] + [4]` → `[1, 2, 3, 4]` (array concatenation)
+- `[1, 2] + [3, 4]` → `[1, 2, 3, 4]` (array concatenation)
+- `{a: 1} + {b: 2}` → `{a: 1, b: 2}` (dict merge)
+- `{a: 1, b: 2} + {b: 99}` → `{a: 1, b: 99}` (dict merge, b overwrites)
+
+**Invalid operations** (throw errors):
+- `true + false` → Error
+- `null + 5` → Error
+- `[1] + 5` → Error
+- `{a: 1} + 5` → Error
 
 #### SUB
 **Stack**: [a, b] → [a - b]
@@ -193,6 +233,62 @@ All arithmetic operations pop two values, perform operation, push result as numb
 #### MOD
 **Stack**: [a, b] → [a % b]
 
+### Bitwise Operations
+
+All bitwise operations coerce operands to 32-bit signed integers, perform the operation, and push the result as a number.
+
+#### BIT_AND
+**Operand**: None
+**Stack**: [a, b] → [a & b]
+
+Performs bitwise AND operation. Both operands are coerced to 32-bit signed integers.
+
+**Example**: `5 & 3` → `1` (binary: `0101 & 0011` → `0001`)
+
+#### BIT_OR
+**Operand**: None
+**Stack**: [a, b] → [a | b]
+
+Performs bitwise OR operation. Both operands are coerced to 32-bit signed integers.
+
+**Example**: `5 | 3` → `7` (binary: `0101 | 0011` → `0111`)
+
+#### BIT_XOR
+**Operand**: None
+**Stack**: [a, b] → [a ^ b]
+
+Performs bitwise XOR (exclusive OR) operation. Both operands are coerced to 32-bit signed integers.
+
+**Example**: `5 ^ 3` → `6` (binary: `0101 ^ 0011` → `0110`)
+
+#### BIT_SHL
+**Operand**: None
+**Stack**: [a, b] → [a << b]
+
+Performs left shift operation. Left operand is coerced to 32-bit signed integer, right operand determines shift amount (masked to 0-31).
+
+**Example**: `5 << 2` → `20` (binary: `0101` shifted left 2 positions → `10100`)
+
+#### BIT_SHR
+**Operand**: None
+**Stack**: [a, b] → [a >> b]
+
+Performs sign-preserving right shift operation. Left operand is coerced to 32-bit signed integer, right operand determines shift amount (masked to 0-31). The sign bit is preserved (arithmetic shift).
+
+**Example**:
+- `20 >> 2` → `5` (binary: `10100` shifted right 2 positions → `0101`)
+- `-20 >> 2` → `-5` (sign bit preserved)
+
+#### BIT_USHR
+**Operand**: None
+**Stack**: [a, b] → [a >>> b]
+
+Performs zero-fill right shift operation. Left operand is coerced to 32-bit signed integer, right operand determines shift amount (masked to 0-31). Zeros are shifted in from the left (logical shift).
+
+**Example**:
+- `-1 >>> 1` → `2147483647` (all bits shift right, zero fills from left)
+- `-8 >>> 1` → `2147483644`
+
 ### Comparison Operations
 
 All comparison operations pop two values, compare, push boolean result.
@@ -231,39 +327,45 @@ All comparison operations pop two values, compare, push boolean result.
 ```
 <evaluate left>
 DUP
-JUMP_IF_FALSE 2    # skip POP and <evaluate right>
+JUMP_IF_FALSE .end
 POP
 <evaluate right>
-end:
+.end:
 ```
 
 **OR pattern** (short-circuits if left side is true):
 ```
 <evaluate left>
 DUP
-JUMP_IF_TRUE 2     # skip POP and <evaluate right>
+JUMP_IF_TRUE .end
 POP
 <evaluate right>
-end:
+.end:
 ```
 
 ### Control Flow
 
 #### JUMP
-**Operand**: Offset (number)
+**Operand**: Label (string)
-**Effect**: Add offset to PC (relative jump)
+**Effect**: Jump to the specified label
 **Stack**: No change
 
+**Note**: JUMP only accepts label operands (`.label`), not numeric offsets. The VM resolves labels to relative offsets internally.
+
 #### JUMP_IF_FALSE
-**Operand**: Offset (number)
+**Operand**: Label (string)
-**Effect**: If top of stack is falsy, add offset to PC (relative jump)
+**Effect**: If top of stack is falsy, jump to the specified label
 **Stack**: [condition] → []
 
+**Note**: JUMP_IF_FALSE only accepts label operands (`.label`), not numeric offsets.
+
 #### JUMP_IF_TRUE
-**Operand**: Offset (number)
+**Operand**: Label (string)
-**Effect**: If top of stack is truthy, add offset to PC (relative jump)
+**Effect**: If top of stack is truthy, jump to the specified label
 **Stack**: [condition] → []
 
+**Note**: JUMP_IF_TRUE only accepts label operands (`.label`), not numeric offsets.
+
 #### BREAK
 **Operand**: None
 **Effect**: Unwind call stack until frame with `isBreakTarget = true`, resume there
@@ -357,15 +459,20 @@ The created function captures `currentScope` as its `parentScope`.
 3. Pop named arguments (name/value pairs) from stack
 4. Pop positional arguments from stack
 5. Pop function from stack
-6. Mark current frame (if exists) as break target (`isBreakTarget = true`)
+6. **If function is native**:
-7. Push new call frame with current PC and scope
+   - Mark current frame (if exists) as break target
-8. Create new scope with function's parentScope as parent
+   - Call native function with positional args
-9. Bind parameters:
+   - Push return value onto stack
+   - Done (skip steps 7-11)
+7. Mark current frame (if exists) as break target (`isBreakTarget = true`)
+8. Push new call frame with current PC and scope
+9. Create new scope with function's parentScope as parent
+10. Bind parameters:
    - For regular functions: bind params by position, then by name, then defaults, then null
    - For variadic functions: bind fixed params, collect rest into array
    - For functions with `named: true`: bind fixed params by position/name, collect unmatched named args into dict
-10. Set currentScope to new scope
+11. Set currentScope to new scope
-11. Jump to function body
+12. Jump to function body
 
 **Parameter Binding Priority** (for fixed params):
 1. Named argument (if provided and matches param name)
@@ -373,12 +480,21 @@ The created function captures `currentScope` as its `parentScope`.
 3. Default value (if defined)
 4. Null
 
+**Null Value Semantics**:
+- Passing `null` as an argument explicitly triggers the default value (if one exists)
+- This allows callers to "opt-in" to defaults even when providing arguments positionally
+- If no default exists, `null` is bound as-is
+- This applies to both ReefVM functions and native TypeScript functions
+- Example: `fn(null, 20)` where `fn(x=10, y)` binds `x=10` (default triggered), `y=20`
+
 **Named Args Handling**:
 - Named args that match fixed parameter names are bound to those params
 - If the function has `named: true`, remaining named args (that don't match any fixed param) are collected into the last parameter as a dict
 - This allows flexible calling: `fn(x=10, y=20, extra=30)` where `extra` goes to the named args dict
+- **Native functions support named arguments** - parameter names are extracted from the function signature at call time
+- Passing `null` via named args also triggers defaults: `fn(x=null)` triggers `x`'s default
 
-**Errors**: Throws if top of stack is not a function
+**Errors**: Throws if top of stack is not a function (or native function)
 
 #### TAIL_CALL
 **Operand**: None
@@ -509,30 +625,190 @@ Key is coerced to string.
 Key is coerced to string.
 **Errors**: Throws if not dict
 
-### TypeScript Interop
+### Unified Access
 
-#### CALL_NATIVE
+#### DOT_GET
-**Operand**: Function name (string)
+**Operand**: None
-**Effect**: Call registered TypeScript function
+**Effect**: Get value from array or dict
-**Stack**: [...args] → [returnValue]
+**Stack**: [array|dict, index|key] → [value]
 
 **Behavior**:
-1. Look up function by name in registry
+- If target is array: coerce index to number and access `array[index]`
-2. Mark current frame (if exists) as break target
+- If target is dict: coerce key to string and access `dict.get(key)`
-3. Await function call (native function receives arguments and returns a Value)
+- Returns null if index out of bounds or key not found
-4. Push return value onto stack
 
-**Notes**:
+**Errors**: Throws if target is not array or dict
-- TypeScript functions are passed the raw stack values as arguments
-- They must return a valid Value
-- They can be async (VM awaits them)
-- Like CALL, but function is from TypeScript registry instead of stack
 
-**Errors**: Throws if function not found
+**Use Cases**:
+- Unified syntax for accessing both arrays and dicts
+- Chaining access operations: `obj.users.0.name`
+- Generic accessor that works with any indexable type
 
-**TypeScript Function Signature**:
+**Example**:
+```
+; Array access
+PUSH 10
+PUSH 20
+PUSH 30
+MAKE_ARRAY #3
+PUSH 1
+DOT_GET           ; → 20
+
+; Dict access
+PUSH 'name'
+PUSH 'Alice'
+MAKE_DICT #1
+PUSH 'name'
+DOT_GET           ; → 'Alice'
+
+; Chained access
+; dict['users'][0]
+LOAD dict
+PUSH 'users'
+DOT_GET
+PUSH 0
+DOT_GET
+```
+
+### String Operations
+
+#### STR_CONCAT
+**Operand**: Number of values to concatenate (number)
+**Effect**: Concatenate N values from stack into a single string
+**Stack**: [val1, val2, ..., valN] → [string]
+
+**Behavior**:
+1. Pop N values from stack (in reverse order)
+2. Convert each value to string using `toString()`
+3. Concatenate all strings in order (val1 + val2 + ... + valN)
+4. Push resulting string onto stack
+
+**Type Coercion**:
+- Numbers → string representation (e.g., `42` → `"42"`)
+- Booleans → `"true"` or `"false"`
+- Null → `"null"`
+- Strings → identity
+- Arrays → `"[item, item]"` format
+- Dicts → `"{key: value, ...}"` format
+- Functions → `"<function>"`
+
+**Use Cases**:
+- Building dynamic strings from multiple parts
+- Template string interpolation
+- String formatting with mixed types
+
+**Composability**:
+- Results can be concatenated again with additional STR_CONCAT operations
+- Can leave values on stack (only consumes specified count)
+
+**Example**:
+```
+PUSH "Hello"
+PUSH " "
+PUSH "World"
+STR_CONCAT #3        ; → "Hello World"
+
+PUSH "Count: "
+PUSH 42
+PUSH ", Active: "
+PUSH true
+STR_CONCAT #4        ; → "Count: 42, Active: true"
+```
+
+**Edge Cases**:
+- `STR_CONCAT #0` produces empty string `""`
+- `STR_CONCAT #1` converts single value to string
+- If stack has fewer values than count, behavior depends on implementation (may use empty strings or throw)
+
+### TypeScript Interop
+
+Native TypeScript functions are registered into the VM's scope and accessed via regular LOAD/CALL operations. They behave identically to Reef functions from the bytecode perspective.
+
+**Registration**:
 ```typescript
-type TypeScriptFunction = (...args: Value[]) => Promise<Value> | Value;
+const vm = new VM(bytecode, {
+  add: (a: number, b: number) => a + b,
+  greet: (name: string) => `Hello, ${name}!`
+})
+
+// Or after construction:
+vm.set('multiply', (a: number, b: number) => a * b)
+```
+
+**Usage in Bytecode**:
+```
+LOAD add          ; Load native function from scope
+PUSH 5
+PUSH 10
+PUSH 2            ; positionalCount
+PUSH 0            ; namedCount
+CALL              ; Call it like any other function
+```
+
+**Native Function Types**:
+
+1. **Auto-wrapped functions** (via `vm.set()`): Accept and return native TypeScript types (number, string, boolean, array, object, etc.). The VM automatically converts between Value types and native types.
+
+2. **Value-based functions** (via `vm.setValueFunction()`): Accept and return `Value` types directly for full control over type handling.
+
+**Auto-Wrapping Behavior**:
+- Parameters: `Value` → native type (number, string, boolean, array, object, null, RegExp)
+- Return value: native type → `Value`
+- Supports sync and async functions
+- Objects convert to dicts, arrays convert to Value arrays
+
+**Named Arguments**:
+- Native functions support named arguments by extracting parameter names from the function signature
+- Parameter binding follows the same priority as Reef functions: named arg > positional arg > default > null
+- TypeScript rest parameters (`...args`) are supported and behave like Reef variadic parameters
+
+**Examples**:
+```typescript
+// Auto-wrapped native types
+vm.set('add', (a: number, b: number) => a + b)
+vm.set('greet', (name: string) => `Hello, ${name}!`)
+vm.set('range', (n: number) => Array.from({ length: n }, (_, i) => i))
+
+// With defaults
+vm.set('greet', (name: string, greeting = 'Hello') => {
+  return `${greeting}, ${name}!`
+})
+
+// Variadic functions
+vm.set('sum', (...nums: number[]) => {
+  return nums.reduce((acc, n) => acc + n, 0)
+})
+
+// Value-based for custom logic
+vm.setValueFunction('customOp', (a: Value, b: Value): Value => {
+  return { type: 'number', value: toNumber(a) + toNumber(b) }
+})
+
+// Async functions
+vm.set('fetchData', async (url: string) => {
+  const response = await fetch(url)
+  return response.json()
+})
+```
+
+**Calling with Named Arguments**:
+```
+; Call with positional args
+LOAD greet
+PUSH "Alice"
+PUSH 1
+PUSH 0
+CALL              ; → "Hello, Alice!"
+
+; Call with named args
+LOAD greet
+PUSH "name"
+PUSH "Bob"
+PUSH "greeting"
+PUSH "Hi"
+PUSH 0
+PUSH 2
+CALL              ; → "Hi, Bob!"
 ```
 
 ### Special
@@ -544,14 +820,16 @@ type TypeScriptFunction = (...args: Value[]) => Promise<Value> | Value;
 
 ## Label Syntax
 
-The bytecode format supports labels for improved readability:
+The bytecode format requires labels for control flow jumps:
 
 **Label Definition**: `.label_name:` marks an instruction position
 **Label Reference**: `.label_name` in operands (e.g., `JUMP .loop_start`)
 
-Labels are resolved to numeric offsets during parsing. The original numeric offset syntax (`#N`) is still supported for backwards compatibility.
+Labels are resolved to relative PC offsets during bytecode compilation. All JUMP instructions (`JUMP`, `JUMP_IF_FALSE`, `JUMP_IF_TRUE`) require label operands.
 
-Example with labels:
+**Note**: Exception handling instructions (`PUSH_TRY`, `PUSH_FINALLY`) and function definitions (`MAKE_FUNCTION`) can use either labels or absolute instruction indices (`#N`).
+
+Example:
 ```
 JUMP .skip
 .middle:
@@ -562,15 +840,6 @@ JUMP .skip
   HALT
 ```
 
-Equivalent with numeric offsets:
-```
-JUMP #2
-PUSH 999
-HALT
-PUSH 42
-HALT
-```
-
 ## Common Bytecode Patterns
 
 ### If-Else Statement
@@ -646,6 +915,29 @@ PUSH 1                # namedCount
 CALL
 ```
 
+### Null Triggering Default Values
+```
+# Function: greet(name='Guest', greeting='Hello')
+MAKE_FUNCTION (name='Guest' greeting='Hello') .greet_body
+STORE 'greet'
+JUMP .main
+.greet_body:
+  LOAD 'greeting'
+  PUSH ', '
+  ADD
+  LOAD 'name'
+  ADD
+  RETURN
+.main:
+  # Call with null for first param - triggers default
+  LOAD 'greet'
+  PUSH null            # name will use default 'Guest'
+  PUSH 'Hi'            # greeting='Hi' (provided)
+  PUSH 2               # positionalCount
+  PUSH 0               # namedCount
+  CALL                 # Returns "Hi, Guest"
+```
+
 ### Tail Recursive Function
 ```
 MAKE_FUNCTION (n acc) .factorial_body
@@ -692,10 +984,9 @@ All of these should throw errors:
 6. **Break Outside Loop**: BREAK with no break target
 7. **Continue Outside Loop**: CONTINUE with no continue target
 8. **Return Outside Function**: RETURN with no call frame
-9. **Unknown Function**: CALL_NATIVE with unregistered function
+9. **Mismatched Handler**: POP_TRY with no handler
-10. **Mismatched Handler**: POP_TRY with no handler
+10. **Invalid Constant**: PUSH with invalid constant index
-11. **Invalid Constant**: PUSH with invalid constant index
+11. **Invalid Function Definition**: MAKE_FUNCTION with non-function_def constant
-12. **Invalid Function Definition**: MAKE_FUNCTION with non-function_def constant
 
 ## Edge Cases
 
@@ -740,11 +1031,21 @@ All of these should throw errors:
 ## VM Initialization
 
 ```typescript
-const vm = new VM(bytecode);
+// Register native functions during construction
-vm.registerFunction('add', (a, b) => {
+const vm = new VM(bytecode, {
+  add: (a: number, b: number) => a + b,
+  greet: (name: string) => `Hello, ${name}!`
+})
+
+// Or register after construction
+vm.set('multiply', (a: number, b: number) => a * b)
+
+// Or use Value-based functions
+vm.setValueFunction('customOp', (a: Value, b: Value): Value => {
   return { type: 'number', value: toNumber(a) + toNumber(b) }
 })
-const result = await vm.execute()
+
+const result = await vm.run()
 ```
 
 ## Testing Considerations

bin/debug

@@ -104,6 +104,8 @@ function formatValue(value: Value): string {
   } else if (value.type === 'function') {
     const params = value.params.join(', ')
     return `${colors.dim}<fn(${params})>${colors.reset}`
+  } else if (value.type === 'native') {
+    return `${colors.dim}<native>${colors.reset}`
   }
   return String(value)
 }

bin/repl

@@ -38,6 +38,8 @@ function formatValue(value: Value): string {
   } else if (value.type === 'function') {
     const params = value.params.join(', ')
     return `${colors.dim}<fn(${params})>${colors.reset}`
+  } else if (value.type === 'native') {
+    return `${colors.dim}<native>${colors.reset}`
   }
   return String(value)
 }

bunfig.toml

@@ -0,0 +1,2 @@
+[test]
+preload = ["./tests/setup.ts"]

examples/add-with-arrays.ts

@@ -0,0 +1,116 @@
+/**
+ * Demonstrates the ADD opcode working with arrays
+ *
+ * ADD now handles array concatenation:
+ * - [1, 2, 3] + [4] === [1, 2, 3, 4]
+ * - If both operands are arrays, they are concatenated
+ */
+
+import { toBytecode, run } from "#reef"
+
+// Basic array concatenation
+const basicConcat = toBytecode([
+  ["PUSH", 1],
+  ["PUSH", 2],
+  ["PUSH", 3],
+  ["MAKE_ARRAY", 3],
+  ["PUSH", 4],
+  ["MAKE_ARRAY", 1],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('Basic array concatenation ([1, 2, 3] + [4]):')
+const result1 = await run(basicConcat)
+console.log(result1)
+// Output: { type: 'array', value: [1, 2, 3, 4] }
+
+// Concatenate two multi-element arrays
+const multiConcat = toBytecode([
+  ["PUSH", 1],
+  ["PUSH", 2],
+  ["MAKE_ARRAY", 2],
+  ["PUSH", 3],
+  ["PUSH", 4],
+  ["MAKE_ARRAY", 2],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nConcatenate two arrays ([1, 2] + [3, 4]):')
+const result2 = await run(multiConcat)
+console.log(result2)
+// Output: { type: 'array', value: [1, 2, 3, 4] }
+
+// Concatenate multiple arrays in sequence
+const multipleConcat = toBytecode([
+  ["PUSH", 1],
+  ["MAKE_ARRAY", 1],
+  ["PUSH", 2],
+  ["MAKE_ARRAY", 1],
+  ["ADD"],
+  ["PUSH", 3],
+  ["MAKE_ARRAY", 1],
+  ["ADD"],
+  ["PUSH", 4],
+  ["MAKE_ARRAY", 1],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nMultiple concatenations ([1] + [2] + [3] + [4]):')
+const result3 = await run(multipleConcat)
+console.log(result3)
+// Output: { type: 'array', value: [1, 2, 3, 4] }
+
+// Concatenate arrays with mixed types
+const mixedTypes = toBytecode([
+  ["PUSH", 1],
+  ["PUSH", "hello"],
+  ["MAKE_ARRAY", 2],
+  ["PUSH", true],
+  ["PUSH", null],
+  ["MAKE_ARRAY", 2],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nConcatenate arrays with mixed types ([1, "hello"] + [true, null]):')
+const result4 = await run(mixedTypes)
+console.log(result4)
+// Output: { type: 'array', value: [1, "hello", true, null] }
+
+// Concatenate empty array with non-empty
+const emptyConcat = toBytecode([
+  ["MAKE_ARRAY", 0],
+  ["PUSH", 1],
+  ["PUSH", 2],
+  ["PUSH", 3],
+  ["MAKE_ARRAY", 3],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nConcatenate empty array with [1, 2, 3] ([] + [1, 2, 3]):')
+const result5 = await run(emptyConcat)
+console.log(result5)
+// Output: { type: 'array', value: [1, 2, 3] }
+
+// Nested arrays
+const nestedConcat = toBytecode([
+  ["PUSH", 1],
+  ["PUSH", 2],
+  ["MAKE_ARRAY", 2],
+  ["MAKE_ARRAY", 1],
+  ["PUSH", 3],
+  ["PUSH", 4],
+  ["MAKE_ARRAY", 2],
+  ["MAKE_ARRAY", 1],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nConcatenate nested arrays ([[1, 2]] + [[3, 4]]):')
+const result6 = await run(nestedConcat)
+console.log(result6)
+// Output: { type: 'array', value: [[1, 2], [3, 4]] }

examples/add-with-dicts.ts

@@ -0,0 +1,158 @@
+/**
+ * Demonstrates the ADD opcode working with dicts
+ *
+ * ADD now handles dict merging:
+ * - {a: 1} + {b: 2} === {a: 1, b: 2}
+ * - If both operands are dicts, they are merged
+ * - Keys from the second dict overwrite keys from the first on conflict
+ */
+
+import { toBytecode, run } from "#reef"
+
+// Basic dict merge
+const basicMerge = toBytecode([
+  ["PUSH", "a"],
+  ["PUSH", 1],
+  ["MAKE_DICT", 1],
+  ["PUSH", "b"],
+  ["PUSH", 2],
+  ["MAKE_DICT", 1],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('Basic dict merge ({a: 1} + {b: 2}):')
+const result1 = await run(basicMerge)
+console.log(result1)
+// Output: { type: 'dict', value: Map { a: 1, b: 2 } }
+
+// Merge with overlapping keys
+const overlapMerge = toBytecode([
+  ["PUSH", "a"],
+  ["PUSH", 1],
+  ["PUSH", "b"],
+  ["PUSH", 2],
+  ["MAKE_DICT", 2],
+  ["PUSH", "b"],
+  ["PUSH", 99],
+  ["PUSH", "c"],
+  ["PUSH", 3],
+  ["MAKE_DICT", 2],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nMerge with overlapping keys ({a: 1, b: 2} + {b: 99, c: 3}):')
+const result2 = await run(overlapMerge)
+console.log(result2)
+console.log('Note: b is overwritten from 2 to 99')
+// Output: { type: 'dict', value: Map { a: 1, b: 99, c: 3 } }
+
+// Merge multiple dicts in sequence
+const multipleMerge = toBytecode([
+  ["PUSH", "a"],
+  ["PUSH", 1],
+  ["MAKE_DICT", 1],
+  ["PUSH", "b"],
+  ["PUSH", 2],
+  ["MAKE_DICT", 1],
+  ["ADD"],
+  ["PUSH", "c"],
+  ["PUSH", 3],
+  ["MAKE_DICT", 1],
+  ["ADD"],
+  ["PUSH", "d"],
+  ["PUSH", 4],
+  ["MAKE_DICT", 1],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nMultiple merges ({a: 1} + {b: 2} + {c: 3} + {d: 4}):')
+const result3 = await run(multipleMerge)
+console.log(result3)
+// Output: { type: 'dict', value: Map { a: 1, b: 2, c: 3, d: 4 } }
+
+// Merge dicts with different value types
+const mixedTypes = toBytecode([
+  ["PUSH", "num"],
+  ["PUSH", 42],
+  ["PUSH", "str"],
+  ["PUSH", "hello"],
+  ["MAKE_DICT", 2],
+  ["PUSH", "bool"],
+  ["PUSH", true],
+  ["PUSH", "null"],
+  ["PUSH", null],
+  ["MAKE_DICT", 2],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nMerge dicts with different types ({num: 42, str: "hello"} + {bool: true, null: null}):')
+const result4 = await run(mixedTypes)
+console.log(result4)
+// Output: { type: 'dict', value: Map { num: 42, str: 'hello', bool: true, null: null } }
+
+// Merge empty dict with non-empty
+const emptyMerge = toBytecode([
+  ["MAKE_DICT", 0],
+  ["PUSH", "x"],
+  ["PUSH", 100],
+  ["PUSH", "y"],
+  ["PUSH", 200],
+  ["MAKE_DICT", 2],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nMerge empty dict with {x: 100, y: 200} ({} + {x: 100, y: 200}):')
+const result5 = await run(emptyMerge)
+console.log(result5)
+// Output: { type: 'dict', value: Map { x: 100, y: 200 } }
+
+// Merge dicts with nested structures
+const nestedMerge = toBytecode([
+  ["PUSH", "data"],
+  ["PUSH", 1],
+  ["PUSH", 2],
+  ["MAKE_ARRAY", 2],
+  ["MAKE_DICT", 1],
+  ["PUSH", "config"],
+  ["PUSH", "debug"],
+  ["PUSH", true],
+  ["MAKE_DICT", 1],
+  ["MAKE_DICT", 1],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nMerge dicts with nested structures:')
+const result6 = await run(nestedMerge)
+console.log(result6)
+// Output: { type: 'dict', value: Map { data: [1, 2], config: { debug: true } } }
+
+// Building configuration objects
+const configBuild = toBytecode([
+  // Default config
+  ["PUSH", "debug"],
+  ["PUSH", false],
+  ["PUSH", "port"],
+  ["PUSH", 3000],
+  ["PUSH", "host"],
+  ["PUSH", "localhost"],
+  ["MAKE_DICT", 3],
+  // Override with user config
+  ["PUSH", "debug"],
+  ["PUSH", true],
+  ["PUSH", "port"],
+  ["PUSH", 8080],
+  ["MAKE_DICT", 2],
+  ["ADD"],
+  ["HALT"]
+])
+
+console.log('\nBuilding config (defaults + overrides):')
+const result7 = await run(configBuild)
+console.log(result7)
+// Output: { type: 'dict', value: Map { debug: true, port: 8080, host: 'localhost' } }

examples/add-with-strings.ts

@@ -0,0 +1,73 @@
+/**
+ * Demonstrates the ADD opcode working with both numbers and strings
+ *
+ * ADD now behaves like JavaScript's + operator:
+ * - If either operand is a string, it does string concatenation
+ * - Otherwise, it does numeric addition
+ */
+
+import { toBytecode, run } from "#reef"
+
+// Numeric addition
+const numericAdd = toBytecode(`
+  PUSH 10
+  PUSH 5
+  ADD
+  HALT
+`)
+
+console.log('Numeric addition (10 + 5):')
+console.log(await run(numericAdd))
+// Output: { type: 'number', value: 15 }
+
+// String concatenation
+const stringConcat = toBytecode(`
+  PUSH "hello"
+  PUSH " world"
+  ADD
+  HALT
+`)
+
+console.log('\nString concatenation ("hello" + " world"):')
+console.log(await run(stringConcat))
+// Output: { type: 'string', value: 'hello world' }
+
+// Mixed: string + number
+const mixedConcat = toBytecode(`
+  PUSH "count: "
+  PUSH 42
+  ADD
+  HALT
+`)
+
+console.log('\nMixed concatenation ("count: " + 42):')
+console.log(await run(mixedConcat))
+// Output: { type: 'string', value: 'count: 42' }
+
+// Building a message
+const buildMessage = toBytecode(`
+  PUSH "You have "
+  PUSH 3
+  ADD
+  PUSH " new messages"
+  ADD
+  HALT
+`)
+
+console.log('\nBuilding a message:')
+console.log(await run(buildMessage))
+// Output: { type: 'string', value: 'You have 3 new messages' }
+
+// Computing then concatenating
+const computeAndConcat = toBytecode(`
+  PUSH "Result: "
+  PUSH 10
+  PUSH 5
+  ADD
+  ADD
+  HALT
+`)
+
+console.log('\nComputing then concatenating ("Result: " + (10 + 5)):')
+console.log(await run(computeAndConcat))
+// Output: { type: 'string', value: 'Result: 15' }

examples/native.ts

@@ -9,7 +9,7 @@ const bytecode = toBytecode(`
 
 const vm = new VM(bytecode)
 
-vm.registerFunction('print', (...args: Value[]): Value => {
+vm.set('print', (...args: Value[]): Value => {
   console.log(...args.map(toString))
   return toNull()
 })

package.json

@@ -1,6 +1,6 @@
 {
   "name": "reefvm",
-  "module": "src/index.ts",
+  "exports": "./src/index.ts",
   "type": "module",
   "scripts": {
     "check": "bunx tsc --noEmit"

src/bytecode.ts

@@ -16,13 +16,15 @@ export type Constant =
   | Value
   | FunctionDef
 
-type Atom = number | string | boolean | null
+type Atom = RegExp | number | string | boolean | null
 
 type InstructionTuple =
   // Stack
   | ["PUSH", Atom]
   | ["POP"]
   | ["DUP"]
+  | ["SWAP"]
+  | ["TYPE"]
 
   // Variables
   | ["LOAD", string]
@@ -32,6 +34,9 @@ type InstructionTuple =
   // Arithmetic
   | ["ADD"] | ["SUB"] | ["MUL"] | ["DIV"] | ["MOD"]
 
+  // Bitwise
+  | ["BIT_AND"] | ["BIT_OR"] | ["BIT_XOR"] | ["BIT_SHL"] | ["BIT_SHR"] | ["BIT_USHR"]
+
   // Comparison
   | ["EQ"] | ["NEQ"] | ["LT"] | ["GT"] | ["LTE"] | ["GTE"]
 
@@ -39,9 +44,9 @@ type InstructionTuple =
   | ["NOT"]
 
   // Control flow
-  | ["JUMP", string | number]
+  | ["JUMP", string]
-  | ["JUMP_IF_FALSE", string | number]
+  | ["JUMP_IF_FALSE", string]
-  | ["JUMP_IF_TRUE", string | number]
+  | ["JUMP_IF_TRUE", string]
   | ["BREAK"]
 
   // Exception handling
@@ -51,7 +56,7 @@ type InstructionTuple =
   | ["THROW"]
 
   // Functions
-  | ["MAKE_FUNCTION", string[], string | number]
+  | ["MAKE_FUNCTION", string[], string]
   | ["CALL"]
   | ["TAIL_CALL"]
   | ["RETURN"]
@@ -70,8 +75,11 @@ type InstructionTuple =
   | ["DICT_SET"]
   | ["DICT_HAS"]
 
-  // Native
+  // Strings
-  | ["CALL_NATIVE", string]
+  | ["STR_CONCAT", number]
+
+  // Arrays and dicts
+  | ["DOT_GET"]
 
   // Special
   | ["HALT"]
@@ -80,30 +88,6 @@ type LabelDefinition = [string] // Just ".label_name:"
 
 export type ProgramItem = InstructionTuple | LabelDefinition
 
-//
-// Parse bytecode from human-readable string format.
-// Operand types are determined by prefix/literal:
-//   #42      -> immediate number (e.g., JUMP #5, MAKE_ARRAY #3)
-//   .label   -> label reference (e.g., JUMP .loop_start, MAKE_FUNCTION (x y) .body)
-//   name     -> variable/function name (e.g., LOAD x, CALL_NATIVE add)
-//   42       -> number constant (e.g., PUSH 42)
-//   "str"    -> string constant (e.g., PUSH "hello")
-//   'str'    -> string constant (e.g., PUSH 'hello')
-//   true     -> boolean constant (e.g., PUSH true)
-//   false    -> boolean constant (e.g., PUSH false)
-//   null     -> null constant (e.g., PUSH null)
-//
-// Labels:
-//   .label_name:   -> label definition (marks current instruction position)
-//
-// Function definitions:
-//   MAKE_FUNCTION (x y) #7           -> basic function (numeric offset)
-//   MAKE_FUNCTION (x y) .body        -> basic function (label reference)
-//   MAKE_FUNCTION (x y=42) #7        -> with defaults
-//   MAKE_FUNCTION (x ...rest) #7     -> variadic
-//   MAKE_FUNCTION (x @named) #7      -> named
-//
-
 function parseFunctionParams(paramStr: string, constants: Constant[]): {
   params: string[]
   defaults: Record<string, number>
@@ -333,12 +317,12 @@ function toBytecodeFromArray(program: ProgramItem[]): Bytecode /* throws */ {
         case "STORE":
         case "TRY_LOAD":
         case "TRY_CALL":
-        case "CALL_NATIVE":
           operandValue = operand as string
           break
 
         case "MAKE_ARRAY":
         case "MAKE_DICT":
+        case "STR_CONCAT":
           operandValue = operand as number
           break
 
@@ -365,6 +349,29 @@ function toBytecodeFromArray(program: ProgramItem[]): Bytecode /* throws */ {
   }
 }
 
+
+////
+// Parse bytecode from human-readable string format.
+// Operand types are determined by prefix/literal:
+//   #42      -> immediate number (e.g., JUMP #5, MAKE_ARRAY #3)
+//   .label   -> label reference (e.g., JUMP .loop_start, MAKE_FUNCTION (x y) .body)
+//   name     -> variable/function name (e.g., LOAD x, LOAD_NATIVE add)
+//   42       -> number constant (e.g., PUSH 42)
+//   "str"    -> string constant (e.g., PUSH "hello")
+//   'str'    -> string constant (e.g., PUSH 'hello')
+//   true     -> boolean constant (e.g., PUSH true)
+//   false    -> boolean constant (e.g., PUSH false)
+//   null     -> null constant (e.g., PUSH null)
+//
+// Labels:
+//   .label_name:   -> label definition (marks current instruction position)
+//
+// Function definitions:
+//   MAKE_FUNCTION (x y) #7           -> basic function (numeric offset)
+//   MAKE_FUNCTION (x y) .body        -> basic function (label reference)
+//   MAKE_FUNCTION (x y=42) #7        -> with defaults
+//   MAKE_FUNCTION (x ...rest) #7     -> variadic
+//   MAKE_FUNCTION (x @named) #7      -> named
 function toBytecodeFromString(str: string): Bytecode /* throws */ {
   const lines = str.trim().split("\n")
 
@@ -383,7 +390,7 @@ function toBytecodeFromString(str: string): Bytecode /* throws */ {
     if (!trimmed) continue
 
     // Check for label definition (.label_name:)
-    if (/^\.[a-zA-Z_][a-zA-Z0-9_]*:$/.test(trimmed)) {
+    if (/^\.[a-zA-Z_][a-zA-Z0-9_.]*:$/.test(trimmed)) {
       const labelName = trimmed.slice(1, -1)
       labels.set(labelName, cleanLines.length)
       continue
@@ -491,6 +498,18 @@ function toBytecodeFromString(str: string): Bytecode /* throws */ {
         bytecode.constants.push(toValue(null))
         operandValue = bytecode.constants.length - 1
 
+      } else if (/^\/.*\/[a-z]*$/.test(operand)) {
+        // regex literal (/pattern/flags)
+        const lastSlash = operand.lastIndexOf('/')
+        const pattern = operand.slice(1, lastSlash)
+        const flags = operand.slice(lastSlash + 1)
+        try {
+          const regex = new RegExp(pattern, flags)
+          bytecode.constants.push(toValue(regex))
+          operandValue = bytecode.constants.length - 1
+        } catch (e) {
+          throw new Error(`Invalid regex literal: ${operand}`)
+        }
       } else {
         // Assume it's a variable name if it doesn't match any other pattern
         // This allows emoji, Unicode, and other creative identifiers

src/format.ts

@@ -0,0 +1,202 @@
+import type { Bytecode, Constant } from "./bytecode"
+import { OpCode } from "./opcode"
+import type { Value, FunctionDef } from "./value"
+
+/**
+ * Converts a Bytecode object back to human-readable string format.
+ * This is the inverse of toBytecode().
+ */
+export const bytecodeToString = (bytecode: Bytecode): string => {
+  const lines: string[] = []
+  const { instructions, constants, labels } = bytecode
+
+  for (let i = 0; i < instructions.length; i++) {
+    // Check if there's a label at this position
+    if (labels?.has(i)) {
+      lines.push(`.${labels.get(i)}:`)
+    }
+
+    const instr = instructions[i]!
+    const opName = OpCode[instr.op] // Get string name from enum
+
+    // Format based on whether operand exists
+    if (instr.operand === undefined) {
+      lines.push(opName)
+    } else {
+      const operandStr = formatOperand(instr.op, instr.operand, constants, labels, i)
+      lines.push(`${opName} ${operandStr}`)
+    }
+  }
+
+  return lines.join('\n')
+}
+
+/**
+ * Format an operand based on the opcode type
+ */
+const formatOperand = (
+  op: OpCode,
+  operand: number | string,
+  constants: Constant[],
+  labels: Map<number, string> | undefined,
+  currentIndex: number
+): string => {
+  // Handle string operands (variable names)
+  if (typeof operand === 'string') {
+    return operand
+  }
+
+  // Handle numeric operands based on opcode
+  switch (op) {
+    case OpCode.PUSH: {
+      // Look up constant value
+      const value = constants[operand]
+      if (!value) {
+        throw new Error(`Invalid constant index: ${operand}`)
+      }
+      return formatConstant(value)
+    }
+
+    case OpCode.MAKE_FUNCTION: {
+      // Look up function definition and format as (params) .label
+      const funcDef = constants[operand]
+      if (!funcDef || !('type' in funcDef) || funcDef.type !== 'function_def') {
+        throw new Error(`Invalid function definition at constant index: ${operand}`)
+      }
+      return formatFunctionDef(funcDef as FunctionDef, labels, constants)
+    }
+
+    case OpCode.JUMP:
+    case OpCode.JUMP_IF_FALSE:
+    case OpCode.JUMP_IF_TRUE: {
+      // Convert relative offset to absolute position
+      const targetIndex = currentIndex + 1 + operand
+      const labelName = labels?.get(targetIndex)
+      return labelName ? `.${labelName}` : `#${operand}`
+    }
+
+    case OpCode.PUSH_TRY:
+    case OpCode.PUSH_FINALLY: {
+      // These use absolute positions
+      const labelName = labels?.get(operand)
+      return labelName ? `.${labelName}` : `#${operand}`
+    }
+
+    case OpCode.MAKE_ARRAY:
+    case OpCode.MAKE_DICT:
+    case OpCode.STR_CONCAT:
+      // These are just counts
+      return `#${operand}`
+
+    default:
+      return `#${operand}`
+  }
+}
+
+/**
+ * Format a constant value (from constants pool)
+ */
+const formatConstant = (constant: Constant): string => {
+  // Handle function definitions (shouldn't happen in PUSH, but be safe)
+  if ('type' in constant && constant.type === 'function_def') {
+    return '<function_def>'
+  }
+
+  // Handle Value types
+  const value = constant as Value
+  switch (value.type) {
+    case 'null':
+      return 'null'
+
+    case 'boolean':
+      return value.value.toString()
+
+    case 'number':
+      return value.value.toString()
+
+    case 'string':
+      // Use single quotes and escape special characters
+      return `'${escapeString(value.value)}'`
+
+    case 'regex': {
+      // Format as /pattern/flags
+      const pattern = value.value.source
+      const flags = value.value.flags
+      return `/${pattern}/${flags}`
+    }
+
+    case 'array': {
+      // Format as [item1, item2, ...]
+      const items = value.value.map(formatConstant).join(', ')
+      return `[${items}]`
+    }
+
+    case 'dict': {
+      // Format as {key1: value1, key2: value2}
+      const entries = Array.from(value.value.entries())
+        .map(([k, v]) => `${k}: ${formatConstant(v)}`)
+        .join(', ')
+      return `{${entries}}`
+    }
+
+    case 'function':
+    case 'native':
+      return '<function>'
+
+    default:
+      return '<unknown>'
+  }
+}
+
+/**
+ * Escape special characters in strings for output
+ */
+const escapeString = (str: string): string => {
+  return str
+    .replace(/\\/g, '\\\\')
+    .replace(/'/g, "\\'")
+    .replace(/\n/g, '\\n')
+    .replace(/\t/g, '\\t')
+    .replace(/\r/g, '\\r')
+    .replace(/\$/g, '\\$')
+}
+
+/**
+ * Format a function definition as (params) .label
+ */
+const formatFunctionDef = (
+  funcDef: FunctionDef,
+  labels: Map<number, string> | undefined,
+  constants: Constant[]
+): string => {
+  const params: string[] = []
+
+  for (let i = 0; i < funcDef.params.length; i++) {
+    const paramName = funcDef.params[i]!
+    const defaultIndex = funcDef.defaults[paramName]
+
+    if (defaultIndex !== undefined) {
+      // Parameter has a default value
+      const defaultValue = constants[defaultIndex]
+      if (!defaultValue) {
+        throw new Error(`Invalid default value index: ${defaultIndex}`)
+      }
+      params.push(`${paramName}=${formatConstant(defaultValue)}`)
+    } else if (i === funcDef.params.length - 1 && funcDef.variadic) {
+      // Last parameter and function is variadic
+      params.push(`...${paramName}`)
+    } else if (i === funcDef.params.length - 1 && funcDef.named) {
+      // Last parameter and function accepts named args
+      params.push(`@${paramName}`)
+    } else {
+      // Regular parameter
+      params.push(paramName)
+    }
+  }
+
+  // Format body address (prefer label name if available)
+  const bodyLabel = labels?.get(funcDef.body)
+  const bodyStr = bodyLabel ? `.${bodyLabel}` : `#${funcDef.body}`
+
+  return `(${params.join(' ')}) ${bodyStr}`
+}

src/function.ts

@@ -0,0 +1,112 @@
+import { type Value, type NativeFunction, fromValue, toValue } from "./value"
+import { VM } from "./vm"
+
+export type ParamInfo = {
+  params: string[]
+  defaults: Record<string, Value>
+  variadic: boolean
+  named: boolean
+}
+
+const WRAPPED_MARKER = Symbol('reef-wrapped')
+
+export function wrapNative(vm: VM, fn: Function): (this: VM, ...args: Value[]) => Promise<Value> {
+  if ((fn as any).raw) return fn as (this: VM, ...args: Value[]) => Promise<Value>
+
+  const wrapped = async function (this: VM, ...values: Value[]) {
+    const nativeArgs = values.map(arg => fromValue(arg, vm))
+    const result = await fn.call(this, ...nativeArgs)
+    return toValue(result, this)
+  }
+
+  const wrappedObj = wrapped as any
+  wrappedObj[WRAPPED_MARKER] = true
+
+  // Store the original function for param extraction
+  wrappedObj.originalFn = fn
+
+  return wrapped
+}
+
+export function isWrapped(fn: Function): boolean {
+  return !!(fn as any)[WRAPPED_MARKER]
+}
+
+export function getOriginalFunction(fn: NativeFunction): Function {
+  return (fn as any).originalFn || fn
+}
+
+export function extractParamInfo(fn: Function): ParamInfo {
+  const params: string[] = []
+  const defaults: Record<string, Value> = {}
+  let variadic = false
+  let named = false
+
+  const fnStr = fn.toString()
+
+  // Match function signature: function(a, b) or (a, b) => or async (a, b) =>
+  const match = fnStr.match(/(?:function\s*.*?\(|^\s*\(|^\s*async\s*\(|^\s*async\s+function\s*.*?\()([^)]*)\)/)
+
+  if (!match || !match[1]) {
+    return { params, defaults, variadic, named }
+  }
+
+  const paramStr = match[1].trim()
+  if (!paramStr) {
+    return { params, defaults, variadic, named }
+  }
+
+  // Split parameters by comma (naive - doesn't handle nested objects/arrays)
+  const paramParts = paramStr.split(',').map(p => p.trim())
+
+  for (const part of paramParts) {
+    // Check for rest parameters (...rest)
+    if (part.startsWith('...')) {
+      variadic = true
+      const paramName = part.slice(3).trim()
+      params.push(paramName)
+    }
+    // Check for default values (name = value)
+    else if (part.includes('=')) {
+      const eqIndex = part.indexOf('=')
+      const paramName = part.slice(0, eqIndex).trim()
+      const defaultStr = part.slice(eqIndex + 1).trim()
+
+      params.push(paramName)
+
+      // Check if this is a named parameter (atXxx pattern)
+      if (/^at[A-Z]/.test(paramName)) {
+        named = true
+      }
+
+      // Try to parse the default value (only simple literals)
+      try {
+        if (defaultStr === 'null') {
+          defaults[paramName] = toValue(null)
+        } else if (defaultStr === 'true') {
+          defaults[paramName] = toValue(true)
+        } else if (defaultStr === 'false') {
+          defaults[paramName] = toValue(false)
+        } else if (/^-?\d+(\.\d+)?$/.test(defaultStr)) {
+          defaults[paramName] = toValue(parseFloat(defaultStr))
+        } else if (/^['"].*['"]$/.test(defaultStr)) {
+          defaults[paramName] = toValue(defaultStr.slice(1, -1))
+        }
+        // For complex defaults (like {}), we skip them and let the function's own default be used
+      } catch {
+        // If parsing fails, ignore the default
+      }
+    } else {
+      // Regular parameter
+      const paramName = part.trim()
+      params.push(paramName)
+
+      // Check if this is a named parameter (atXxx pattern)
+      if (/^at[A-Z]/.test(paramName)) {
+        named = true
+      }
+    }
+  }
+
+  return { params, defaults, variadic, named }
+}

src/index.ts

@@ -1,12 +1,17 @@
 import type { Bytecode } from "./bytecode"
-import { type Value } from "./value"
+import type { Value } from "./value"
 import { VM } from "./vm"
 
-export async function run(bytecode: Bytecode): Promise<Value> {
+export async function run(bytecode: Bytecode, globals?: Record<string, any>): Promise<Value> {
-  const vm = new VM(bytecode)
+  const vm = new VM(bytecode, globals)
   return await vm.run()
 }
 
-export { type Bytecode, toBytecode } from "./bytecode"
+export { type Bytecode, toBytecode, type ProgramItem } from "./bytecode"
-export { type Value, toValue, toString, toNumber, fromValue, toNull, wrapNative } from "./value"
+export { bytecodeToString } from "./format"
+export { wrapNative, isWrapped, type ParamInfo, extractParamInfo, getOriginalFunction } from "./function"
+export { OpCode } from "./opcode"
+export { Scope } from "./scope"
+export type { Value, TypeScriptFunction, NativeFunction } from "./value"
+export { isValue, toValue, toString, toNumber, fromValue, toNull, fnFromValue } from "./value"
 export { VM } from "./vm"

src/opcode.ts

@@ -3,12 +3,16 @@ export enum OpCode {
   PUSH,  // operand: constant index (number) | stack: [] → [value]
   POP,   // operand: none | stack: [value] → []
   DUP,   // operand: none | stack: [value] → [value, value]
+  SWAP,  // operand: none | stack: [value1, value2] → [value2, value1]
 
   // variables
   LOAD,     // operand: variable name (identifier) | stack: [] → [value]
   STORE,    // operand: variable name (identifier) | stack: [value] → []
   TRY_LOAD, // operand: variable name (identifier) | stack: [] → [value] | load a variable (if found) or a string
 
+  // information
+  TYPE,      // operand: none | stack: [a] → []
+
   // math (coerce to number, pop 2, push result)
   ADD,   // operand: none | stack: [a, b] → [a + b]
   SUB,   // operand: none | stack: [a, b] → [a - b]
@@ -16,6 +20,14 @@ export enum OpCode {
   DIV,   // operand: none | stack: [a, b] → [a / b]
   MOD,   // operand: none | stack: [a, b] → [a % b]
 
+  // bitwise operations (coerce to 32-bit integers, pop 2, push result)
+  BIT_AND,   // operand: none | stack: [a, b] → [a & b]
+  BIT_OR,    // operand: none | stack: [a, b] → [a | b]
+  BIT_XOR,   // operand: none | stack: [a, b] → [a ^ b]
+  BIT_SHL,   // operand: none | stack: [a, b] → [a << b]
+  BIT_SHR,   // operand: none | stack: [a, b] → [a >> b] (sign-preserving)
+  BIT_USHR,  // operand: none | stack: [a, b] → [a >>> b] (zero-fill)
+
   // comparison (pop 2, push boolean)
   EQ,    // operand: none | stack: [a, b] → [a == b] (deep equality)
   NEQ,   // operand: none | stack: [a, b] → [a != b]
@@ -59,8 +71,11 @@ export enum OpCode {
   DICT_SET,    // operand: none | stack: [dict, key, value] → [] | mutates dict
   DICT_HAS,    // operand: none | stack: [dict, key] → [boolean]
 
-  // typescript interop
+  // arrays and dicts
-  CALL_NATIVE, // operand: function name (identifier) | stack: [...args] → [result] | consumes entire stack
+  DOT_GET,     // operand: none | stack: [array|dict, index|key] → [value] | unified accessor, returns null if missing
+
+  // strings
+  STR_CONCAT,  // operand: value count (number) | stack: [val1, ..., valN] → [string] | concatenate N values
 
   // special
   HALT         // operand: none | stop execution

src/scope.ts

@@ -30,6 +30,15 @@ export class Scope {
   has(name: string): boolean {
     return this.locals.has(name) || this.parent?.has(name) || false
   }
+
+  vars(): string[] {
+    const vars = new Set(this.parent?.vars())
+
+    for (const name of this.locals.keys())
+      vars.add(name)
+
+    return [...vars].sort()
+  }
 }
 
 

src/validator.ts

@@ -43,18 +43,26 @@ const OPCODES_WITH_OPERANDS = new Set([
   OpCode.PUSH_FINALLY,
   OpCode.MAKE_ARRAY,
   OpCode.MAKE_DICT,
+  OpCode.STR_CONCAT,
   OpCode.MAKE_FUNCTION,
-  OpCode.CALL_NATIVE,
 ])
 
 const OPCODES_WITHOUT_OPERANDS = new Set([
   OpCode.POP,
   OpCode.DUP,
+  OpCode.SWAP,
+  OpCode.TYPE,
   OpCode.ADD,
   OpCode.SUB,
   OpCode.MUL,
   OpCode.DIV,
   OpCode.MOD,
+  OpCode.BIT_AND,
+  OpCode.BIT_OR,
+  OpCode.BIT_XOR,
+  OpCode.BIT_SHL,
+  OpCode.BIT_SHR,
+  OpCode.BIT_USHR,
   OpCode.EQ,
   OpCode.NEQ,
   OpCode.LT,
@@ -76,13 +84,18 @@ const OPCODES_WITHOUT_OPERANDS = new Set([
   OpCode.DICT_GET,
   OpCode.DICT_SET,
   OpCode.DICT_HAS,
+  OpCode.DOT_GET,
 ])
 
-// immediate = immediate number, eg #5
+// JUMP* instructions require labels only (no numeric immediates)
-const OPCODES_REQUIRING_IMMEDIATE_OR_LABEL = new Set([
+const OPCODES_REQUIRING_LABEL = new Set([
   OpCode.JUMP,
   OpCode.JUMP_IF_FALSE,
   OpCode.JUMP_IF_TRUE,
+])
+
+// PUSH_TRY/PUSH_FINALLY still allow immediate or label
+const OPCODES_REQUIRING_IMMEDIATE_OR_LABEL = new Set([
   OpCode.PUSH_TRY,
   OpCode.PUSH_FINALLY,
 ])
@@ -91,6 +104,7 @@ const OPCODES_REQUIRING_IMMEDIATE_OR_LABEL = new Set([
 const OPCODES_REQUIRING_IMMEDIATE = new Set([
   OpCode.MAKE_ARRAY,
   OpCode.MAKE_DICT,
+  OpCode.STR_CONCAT,
 ])
 
 export function validateBytecode(source: string): ValidationResult {
@@ -187,6 +201,16 @@ export function validateBytecode(source: string): ValidationResult {
 
     // Validate specific operand formats
     if (operand) {
+      if (OPCODES_REQUIRING_LABEL.has(opCode)) {
+        if (!operand.startsWith('.')) {
+          errors.push({
+            line: lineNum,
+            message: `${opName} requires label (.label), got: ${operand}`,
+          })
+          continue
+        }
+      }
+
       if (OPCODES_REQUIRING_IMMEDIATE_OR_LABEL.has(opCode)) {
         if (!operand.startsWith('#') && !operand.startsWith('.')) {
           errors.push({
@@ -300,11 +324,11 @@ export function validateBytecode(source: string): ValidationResult {
           }
         }
 
-        // Validate body address
+        // Validate body address (must be a label)
-        if (!bodyAddr!.startsWith('.') && !bodyAddr!.startsWith('#')) {
+        if (!bodyAddr!.startsWith('.')) {
           errors.push({
             line: lineNum,
-            message: `Invalid body address: expected .label or #offset`,
+            message: `Invalid body address: expected .label, got: ${bodyAddr}`,
           })
         }
 

src/value.ts

@@ -1,4 +1,12 @@
+import { wrapNative, getOriginalFunction } from "./function"
+import { OpCode } from "./opcode"
 import { Scope } from "./scope"
+import { VM } from "./vm"
+
+export type NativeFunction = (...args: Value[]) => Promise<Value> | Value
+export type TypeScriptFunction = (this: VM, ...args: any[]) => any
+const REEF_FUNCTION = Symbol('__reefFunction')
+const VALUE_TYPES = new Set(['null', 'boolean', 'number', 'string', 'array', 'dict', 'regex', 'native', 'function'])
 
 export type Value =
   | { type: 'null', value: null }
@@ -7,6 +15,8 @@ export type Value =
   | { type: 'string', value: string }
   | { type: 'array', value: Value[] }
   | { type: 'dict', value: Dict }
+  | { type: 'regex', value: RegExp }
+  | { type: 'native', fn: NativeFunction, value: '<function>' }
   | {
     type: 'function',
     params: string[],
@@ -29,15 +39,22 @@ export type FunctionDef = {
   named: boolean
 }
 
-export function toValue(v: any): Value /* throws */ {
+export function isValue(v: any): boolean {
+  return !!(v && typeof v === 'object' && VALUE_TYPES.has(v.type) && 'value' in v)
+}
+
+export function toValue(v: any, vm?: VM): Value /* throws */ {
   if (v === null || v === undefined)
     return { type: 'null', value: null }
 
-  if (v && typeof v === 'object' && 'type' in v && 'value' in v)
+  if (isValue(v))
     return v as Value
 
   if (Array.isArray(v))
-    return { type: 'array', value: v.map(toValue) }
+    return { type: 'array', value: v.map(x => toValue(x, vm)) }
+
+  if (v instanceof RegExp)
+    return { type: 'regex', value: v }
 
   switch (typeof v) {
     case 'boolean':
@@ -47,28 +64,53 @@ export function toValue(v: any): Value /* throws */ {
     case 'string':
       return { type: 'string', value: v }
     case 'function':
-      throw "can't toValue() a js function yet"
+      if ((v as any)[REEF_FUNCTION])
+        return (v as any)[REEF_FUNCTION]
+
+      let fn = vm ? wrapNative(vm, v) : cantCallFunctionWithoutVM(v)
+      return { type: 'native', fn, value: '<function>' }
     case 'object':
       const dict: Dict = new Map()
 
-      for (const key of Object.keys(v))
+      for (const key of Object.keys(v)) dict.set(key, toValue(v[key], vm))
-        dict.set(key, toValue(v[key]))
 
       return { type: 'dict', value: dict }
     default:
-      throw `can't toValue this: ${v}`
+      throw new Error(`can't toValue this: ${v}`)
+  }
+}
+
+function cantCallFunctionWithoutVM(fn: Function) {
+  const name = fn.name || '<anonymous>'
+  const str = fn.toString().slice(0, 100)
+  return (...args: Value[]) => {
+    const stack = new Error().stack || ''
+    const stackLines = stack.split('\n')
+      .slice(1)
+      .filter(line => !line.includes('toValue'))
+      .map(line => '    ' + line.trim())
+      .join('\n')
+    throw new Error(
+      `can't call function that was converted without a vm\n` +
+      `  Function: ${name}\n` +
+      `  Source: ${str}${str.length > 100 ? '...' : ''}\n` +
+      `  Called from:\n${stackLines}`
+    )
   }
 }
 
 export function toNumber(v: Value): number {
   switch (v.type) {
-    case 'number': return v.value
+    case 'number':
-    case 'boolean': return v.value ? 1 : 0
+      return v.value
+    case 'boolean':
+      return v.value ? 1 : 0
     case 'string': {
       const parsed = parseFloat(v.value)
       return isNaN(parsed) ? 0 : parsed
     }
-    default: return 0
+    default:
+      return 0
   }
 }
 
@@ -85,17 +127,28 @@ export function isTrue(v: Value): boolean {
 
 export function toString(v: Value): string {
   switch (v.type) {
-    case 'string': return v.value
+    case 'string':
-    case 'number': return String(v.value)
+      return v.value
-    case 'boolean': return String(v.value)
+    case 'number':
-    case 'null': return 'null'
+      return String(v.value)
-    case 'function': return '<function>'
+    case 'boolean':
-    case 'array': return `[${v.value.map(toString).join(', ')}]`
+      return String(v.value)
+    case 'null':
+      return 'null'
+    case 'function':
+      return '<function>'
+    case 'native':
+      return '<function>'
+    case 'array':
+      return `[${v.value.map(toString).join(', ')}]`
     case 'dict': {
-      const pairs = Array.from(v.value.entries())
+      const pairs = Array.from(v.value.entries()).map(([k, v]) => `${k}: ${toString(v)}`)
-        .map(([k, v]) => `${k}: ${toString(v)}`)
       return `{${pairs.join(', ')}}`
     }
+    case 'regex':
+      return String(v.value)
+    default:
+      return String(v)
   }
 }
 
@@ -103,10 +156,12 @@ export function isEqual(a: Value, b: Value): boolean {
   if (a.type !== b.type) return false
 
   switch (a.type) {
-    case 'null': return true
+    case 'null':
-    case 'boolean': return a.value === (b as typeof a).value
+      return true
-    case 'number': return a.value === (b as typeof a).value
+    case 'boolean':
-    case 'string': return a.value === (b as typeof a).value
+    case 'number':
+    case 'string':
+      return a.value === b.value
     case 'array': {
       const bArr = b as typeof a
       if (a.value.length !== bArr.value.length) return false
@@ -121,19 +176,48 @@ export function isEqual(a: Value, b: Value): boolean {
       }
       return true
     }
-    case 'function': return false // functions never equal
+    case 'regex': {
+      return String(a.value) === String(b.value)
+    }
+    case 'function':
+    case 'native':
+      return false // functions never equal
+    default:
+      return false
   }
 }
 
-export function fromValue(v: Value): any {
+export function fromValue(v: Value, vm?: VM): any {
   switch (v.type) {
-    case 'null': return null
+    case 'null':
-    case 'boolean': return v.value
+    case 'boolean':
-    case 'number': return v.value
+    case 'number':
-    case 'string': return v.value
+    case 'string':
-    case 'array': return v.value.map(fromValue)
+      return v.value
-    case 'dict': return Object.fromEntries(v.value.entries().map(([k, v]) => [k, fromValue(v)]))
+    case 'array':
-    case 'function': return '<function>'
+      return v.value.map(x => fromValue(x, vm))
+    case 'dict':
+      return Object.fromEntries(v.value.entries().map(([k, v]) => [k, fromValue(v, vm)]))
+    case 'regex':
+      return v.value
+    case 'function':
+      if (!vm || !(vm instanceof VM)) {
+        const stack = new Error().stack || ''
+        const stackLines = stack.split('\n')
+          .slice(1)
+          .filter(line => !line.includes('fromValue'))
+          .map(line => '    ' + line.trim())
+          .join('\n')
+        throw new Error(
+          `VM is required for function conversion\n` +
+          `  Function params: [${v.params.join(', ')}]\n` +
+          `  Function body at instruction: ${v.body}\n` +
+          `  Called from:\n${stackLines}`
+        )
+      }
+      return fnFromValue(v, vm)
+    case 'native':
+      return getOriginalFunction(v.fn)
   }
 }
 
@@ -141,21 +225,49 @@ export function toNull(): Value {
   return toValue(null)
 }
 
-const WRAPPED_MARKER = Symbol('reef-wrapped')
+export function fnFromValue(fn: Value, vm: VM): Function {
+  if (fn.type !== 'function')
+    throw new Error('Value is not a function')
 
-export function wrapNative(fn: Function): (...args: Value[]) => Promise<Value> {
+  const wrapper = async function (...args: any[]) {
-  const wrapped = async (...values: Value[]) => {
+    let positional: any[] = args
-    const nativeArgs = values.map(fromValue)
+    let named: Record<string, any> = {}
-    const result = await fn(...nativeArgs)
+
-    return toValue(result)
+    if (args.length > 0 && !Array.isArray(args[args.length - 1]) && args[args.length - 1].constructor === Object) {
+      named = args[args.length - 1]
+      positional = args.slice(0, -1)
+    }
+
+    const newVM = new VM({
+      instructions: vm.instructions,
+      constants: vm.constants,
+      labels: vm.labels
+    })
+    newVM.scope = fn.parentScope
+
+    newVM.stack.push(fn)
+    newVM.stack.push(...positional.map(x => toValue(x, vm)))
+    for (const [key, val] of Object.entries(named)) {
+      newVM.stack.push(toValue(key))
+      newVM.stack.push(toValue(val, vm))
+    }
+    newVM.stack.push(toValue(positional.length))
+    newVM.stack.push(toValue(Object.keys(named).length))
+
+    const targetDepth = newVM.callStack.length
+    await newVM.execute({ op: OpCode.CALL })
+    newVM.pc++
+
+    while (newVM.callStack.length > targetDepth && newVM.pc < newVM.instructions.length) {
+      await newVM.execute(newVM.instructions[newVM.pc]!)
+      newVM.pc++
+    }
+
+    return fromValue(newVM.stack.pop() || toNull(), vm)
   }
 
-  const wrappedObj = wrapped as any
+    // support roundtrips, eg fromValue(toValue(fn))
-  wrappedObj[WRAPPED_MARKER] = true
+    ; (wrapper as any)[REEF_FUNCTION] = fn
 
-  return wrapped
+  return wrapper
-}
-
-export function isWrapped(fn: Function): boolean {
-  return !!(fn as any)[WRAPPED_MARKER]
 }

src/vm.ts

@@ -3,9 +3,9 @@ import type { ExceptionHandler } from "./exception"
 import { type Frame } from "./frame"
 import { OpCode } from "./opcode"
 import { Scope } from "./scope"
-import { type Value, toValue, toNumber, isTrue, isEqual, toString, wrapNative, isWrapped } from "./value"
+import type { Value, NativeFunction, TypeScriptFunction } from "./value"
-
+import { toValue, toNumber, isTrue, isEqual, toString, fromValue, fnFromValue } from "./value"
-type NativeFunction = (...args: Value[]) => Promise<Value> | Value
+import { extractParamInfo, getOriginalFunction } from "./function"
 
 export class VM {
   pc = 0
@@ -19,20 +19,69 @@ export class VM {
   labels: Map<number, string> = new Map()
   nativeFunctions: Map<string, NativeFunction> = new Map()
 
-  constructor(bytecode: Bytecode) {
+  constructor(bytecode: Bytecode, globals?: Record<string, any>) {
     this.instructions = bytecode.instructions
     this.constants = bytecode.constants
     this.labels = bytecode.labels || new Map()
     this.scope = new Scope()
+
+    if (globals) {
+      for (const name of Object.keys(globals ?? {}))
+        this.set(name, globals[name])
+
+      this.scope = new Scope(this.scope)
+    }
   }
 
-  registerFunction(name: string, fn: Function) {
+  async call(name: string, ...args: any) {
-    const wrapped = isWrapped(fn) ? fn as NativeFunction : wrapNative(fn)
+    const value = this.scope.get(name)
-    this.nativeFunctions.set(name, wrapped)
+
+    if (!value) throw new Error(`Can't find ${name}`)
+    if (value.type !== 'function' && value.type !== 'native')
+      throw new Error(`Can't call ${name}`)
+
+    if (value.type === 'native') {
+      return await this.callNative(value.fn, args)
+    } else {
+      const fn = fnFromValue(value, this)
+      return await fn(...args)
+    }
   }
 
-  registerValueFunction(name: string, fn: NativeFunction) {
+  has(name: string): boolean {
-    this.nativeFunctions.set(name, fn)
+    return this.scope.has(name)
+  }
+
+  vars(): string[] {
+    return this.scope.vars()
+  }
+
+  get(name: string) {
+    return this.scope.get(name)
+  }
+
+  set(name: string, value: any) {
+    this.scope.set(name, toValue(value, this))
+  }
+
+  setFunction(name: string, fn: TypeScriptFunction) {
+    this.scope.set(name, toValue(fn, this))
+  }
+
+  setValueFunction(name: string, fn: NativeFunction) {
+    this.scope.set(name, { type: 'native', fn, value: '<function>' })
+  }
+
+  pushScope(locals?: Record<string, any>) {
+    this.scope = new Scope(this.scope)
+
+    if (locals)
+      for (const [name, value] of Object.entries(locals))
+        this.set(name, value)
+  }
+
+  popScope() {
+    this.scope = this.scope.parent!
   }
 
   async run(): Promise<Value> {
@@ -48,6 +97,57 @@ export class VM {
     return this.stack[this.stack.length - 1] || toValue(null)
   }
 
+  // Resume execution from current PC without resetting
+  // Useful for REPL mode where you append bytecode incrementally
+  async continue(): Promise<Value> {
+    this.stopped = false
+
+    while (!this.stopped && this.pc < this.instructions.length) {
+      const instruction = this.instructions[this.pc]!
+      await this.execute(instruction)
+      this.pc++
+    }
+
+    return this.stack[this.stack.length - 1] || toValue(null)
+  }
+
+  // Helper for REPL mode: append new bytecode with proper constant index remapping
+  appendBytecode(bytecode: Bytecode): void {
+    const constantOffset = this.constants.length
+    const instructionOffset = this.instructions.length
+
+    // Remap function body addresses in constants before adding them
+    for (const constant of bytecode.constants) {
+      if (constant.type === 'function_def') {
+        this.constants.push({ ...constant, body: constant.body + instructionOffset })
+      } else {
+        this.constants.push(constant)
+      }
+    }
+
+    for (const instruction of bytecode.instructions) {
+      if (instruction.operand !== undefined && typeof instruction.operand === 'number') {
+        // Opcodes that reference constants need their operand adjusted
+        if (instruction.op === OpCode.PUSH || instruction.op === OpCode.MAKE_FUNCTION) {
+          this.instructions.push({
+            op: instruction.op,
+            operand: instruction.operand + constantOffset
+          })
+        } else {
+          this.instructions.push(instruction)
+        }
+      } else {
+        this.instructions.push(instruction)
+      }
+    }
+
+    if (bytecode.labels) {
+      for (const [addr, label] of bytecode.labels.entries()) {
+        this.labels.set(addr + instructionOffset, label)
+      }
+    }
+  }
+
   async execute(instruction: Instruction) /* throws */ {
     switch (instruction.op) {
       case OpCode.PUSH:
@@ -68,8 +168,32 @@ export class VM {
         this.stack.push(this.stack[this.stack.length - 1]!)
         break
 
+      case OpCode.SWAP:
+        const first = this.stack.pop()!
+        const second = this.stack.pop()!
+        this.stack.push(first)
+        this.stack.push(second)
+        break
+
       case OpCode.ADD:
-        this.binaryOp((a, b) => toNumber(a) + toNumber(b))
+        const b = this.stack.pop()!
+        const a = this.stack.pop()!
+
+        if (a.type === 'string' || b.type === 'string') {
+          this.stack.push(toValue(toString(a) + toString(b)))
+        } else if (a.type === 'array' && b.type === 'array') {
+          this.stack.push({ type: 'array', value: [...a.value, ...b.value] })
+        } else if (a.type === 'dict' && b.type === 'dict') {
+          const merged = new Map(a.value)
+          for (const [key, value] of b.value) {
+            merged.set(key, value)
+          }
+          this.stack.push({ type: 'dict', value: merged })
+        } else if (a.type === 'number' && b.type === 'number') {
+          this.stack.push(toValue(a.value + b.value))
+        } else {
+          throw new Error(`ADD: Cannot add ${a.type} and ${b.type}`)
+        }
         break
 
       case OpCode.SUB:
@@ -117,6 +241,31 @@ export class VM {
         this.stack.push({ type: 'boolean', value: !isTrue(val) })
         break
 
+      // Bitwise operations
+      case OpCode.BIT_AND:
+        this.binaryOp((a, b) => (toNumber(a) | 0) & (toNumber(b) | 0))
+        break
+
+      case OpCode.BIT_OR:
+        this.binaryOp((a, b) => (toNumber(a) | 0) | (toNumber(b) | 0))
+        break
+
+      case OpCode.BIT_XOR:
+        this.binaryOp((a, b) => (toNumber(a) | 0) ^ (toNumber(b) | 0))
+        break
+
+      case OpCode.BIT_SHL:
+        this.binaryOp((a, b) => (toNumber(a) | 0) << (toNumber(b) | 0))
+        break
+
+      case OpCode.BIT_SHR:
+        this.binaryOp((a, b) => (toNumber(a) | 0) >> (toNumber(b) | 0))
+        break
+
+      case OpCode.BIT_USHR:
+        this.binaryOp((a, b) => (toNumber(a) | 0) >>> (toNumber(b) | 0))
+        break
+
       case OpCode.HALT:
         this.stopped = true
         break
@@ -137,13 +286,18 @@ export class VM {
         const value = this.scope.get(varName)
 
         if (value === undefined)
-          this.stack.push(toValue(varName))
+          this.stack.push(toValue(varName, this))
         else
           this.stack.push(value)
 
         break
       }
 
+      case OpCode.TYPE:
+        const value = this.stack.pop()!
+        this.stack.push(toValue(value.type))
+        break
+
       case OpCode.STORE:
         const name = instruction.operand as string
         const toStore = this.stack.pop()!
@@ -334,6 +488,32 @@ export class VM {
         this.stack.push({ type: 'boolean', value: hasDict.value.has(toString(hasKey)) })
         break
 
+      case OpCode.DOT_GET: {
+        const index = this.stack.pop()!
+        const target = this.stack.pop()!
+
+        if (target.type === 'array')
+          this.stack.push(toValue(target.value?.[Number(index.value)], this))
+
+        else if (target.type === 'dict')
+          this.stack.push(toValue(target.value?.get(String(index.value)), this))
+
+        else
+          throw new Error(`DOT_GET: ${target.type} not supported`)
+
+        break
+      }
+
+      case OpCode.STR_CONCAT:
+        let count = instruction.operand as number
+        let parts = []
+
+        while (count-- > 0 && this.stack.length)
+          parts.unshift(toString(this.stack.pop()!))
+
+        this.stack.push(toValue(parts.join('')))
+        break
+
       case OpCode.MAKE_FUNCTION:
         const fnDefIdx = instruction.operand as number
         const fnDef = this.constants[fnDefIdx]
@@ -353,16 +533,17 @@ export class VM {
         })
         break
 
-      // @ts-ignore
       case OpCode.TRY_CALL: {
         const varName = instruction.operand as string
         const value = this.scope.get(varName)
 
-        if (value?.type === 'function') {
+        if (value?.type === 'function' || value?.type === 'native') {
           this.stack.push(value)
           this.stack.push(toValue(0))
           this.stack.push(toValue(0))
-          // No `break` here -- we want to fall through to OpCode.CALL!
+          this.instructions[this.pc] = { op: OpCode.CALL }
+          this.pc--
+          break
         } else if (value) {
           this.stack.push(value)
           break
@@ -372,8 +553,6 @@ export class VM {
         }
       }
 
-      // don't put any `case` statement here - `TRY_CALL` MUST go before `CALL!`
-
       case OpCode.CALL: {
         // Pop named count from stack (top)
         const namedCount = toNumber(this.stack.pop()!)
@@ -391,9 +570,8 @@ export class VM {
           const key = this.stack.pop()!
           namedPairs.unshift({ key: toString(key), value })
         }
-        for (const pair of namedPairs) {
+        for (const pair of namedPairs)
           namedArgs.set(pair.key, pair.value)
-        }
 
         // Pop positional arguments from stack
         const positionalArgs: Value[] = []
@@ -402,8 +580,110 @@ export class VM {
 
         const fn = this.stack.pop()!
 
+        // Handle native functions
+        if (fn.type === 'native') {
+          // Mark current frame as break target (like regular CALL does)
+          if (this.callStack.length > 0)
+            this.callStack[this.callStack.length - 1]!.isBreakTarget = true
+
+          // Extract parameter info on-demand
+          const originalFn = getOriginalFunction(fn.fn)
+          const paramInfo = extractParamInfo(originalFn)
+
+          // Bind parameters using the same priority as Reef functions
+          const nativeArgs: Value[] = []
+
+          // Determine how many params are fixed (excluding variadic and named)
+          let nativeFixedParamCount = paramInfo.params.length
+          if (paramInfo.variadic) nativeFixedParamCount--
+          if (paramInfo.named) nativeFixedParamCount--
+
+          // Track which positional args have been consumed
+          let nativePositionalArgIndex = 0
+
+          // Bind fixed parameters using priority: named arg > positional arg > default > null
+          // Note: null values trigger defaults (null acts as "use default")
+          for (let i = 0; i < nativeFixedParamCount; i++) {
+            const paramName = paramInfo.params[i]!
+            let paramValue: Value | undefined
+
+            // Check if named argument was provided for this param
+            if (namedArgs.has(paramName)) {
+              paramValue = namedArgs.get(paramName)!
+              namedArgs.delete(paramName) // Remove from named args so it won't go to @named
+            } else if (nativePositionalArgIndex < positionalArgs.length) {
+              paramValue = positionalArgs[nativePositionalArgIndex]!
+              nativePositionalArgIndex++
+            }
+
+            // If the parameter value is null and a default exists, use the default
+            if (paramValue?.type === 'null' && paramInfo.defaults[paramName] !== undefined) {
+              nativeArgs.push(paramInfo.defaults[paramName]!)
+            } else if (paramValue) {
+              nativeArgs.push(paramValue)
+            } else if (paramInfo.defaults[paramName] !== undefined) {
+              nativeArgs.push(paramInfo.defaults[paramName]!)
+            } else {
+              nativeArgs.push(toValue(null))
+            }
+          }
+
+          // Handle named parameter (collect remaining unmatched named args)
+          // Parameter names matching atXxx pattern (e.g., atOptions, atNamed) collect extra named args
+          if (paramInfo.named) {
+            const namedDict = new Map<string, Value>()
+            for (const [key, value] of namedArgs) {
+              namedDict.set(key, value)
+            }
+            // Convert dict to plain JavaScript object for the native function
+            const namedObj = fromValue({ type: 'dict', value: namedDict }, this)
+            nativeArgs.push(toValue(namedObj, this))
+          }
+
+          // Handle variadic parameter (TypeScript rest parameters)
+          // For TypeScript functions with ...rest, we spread the remaining args
+          // rather than wrapping them in an array
+          if (paramInfo.variadic) {
+            const remainingArgs = positionalArgs.slice(nativePositionalArgIndex)
+            nativeArgs.push(...remainingArgs)
+          }
+
+          // Call the native function with bound args
+          try {
+            const result = await fn.fn.call(this, ...nativeArgs)
+            this.stack.push(result)
+            break
+          } catch (error) {
+            const errorMessage = error instanceof Error ? error.message : String(error)
+            const errorValue = toValue(errorMessage)
+
+            // no exception handlers, let it crash
+            if (this.exceptionHandlers.length === 0) {
+              throw new Error(errorMessage)
+            }
+
+            // use existing THROW logic
+            const throwHandler = this.exceptionHandlers.pop()!
+
+            while (this.callStack.length > throwHandler.callStackDepth)
+              this.callStack.pop()
+
+            this.scope = throwHandler.scope
+            this.stack.push(errorValue)
+
+            // Jump to `finally` if present, otherwise jump to `catch`
+            const targetAddress = throwHandler.finallyAddress !== undefined
+              ? throwHandler.finallyAddress
+              : throwHandler.catchAddress
+
+            // subtract 1 because pc will be incremented
+            this.pc = targetAddress - 1
+            break
+          }
+        }
+
         if (fn.type !== 'function')
-          throw new Error('CALL: not a function')
+          throw new Error(`CALL: ${fn.value} is not a function`)
 
         if (this.callStack.length > 0)
           this.callStack[this.callStack.length - 1]!.isBreakTarget = true
@@ -421,16 +701,33 @@ export class VM {
         if (fn.variadic) fixedParamCount--
         if (fn.named) fixedParamCount--
 
+        // Track which positional args have been consumed
+        let positionalArgIndex = 0
+
         // Bind fixed parameters using priority: named arg > positional arg > default > null
+        // Note: null values trigger defaults (null acts as "use default")
         for (let i = 0; i < fixedParamCount; i++) {
           const paramName = fn.params[i]!
+          let paramValue: Value | undefined
 
           // Check if named argument was provided for this param
           if (namedArgs.has(paramName)) {
-            this.scope.set(paramName, namedArgs.get(paramName)!)
+            paramValue = namedArgs.get(paramName)!
             namedArgs.delete(paramName) // Remove from named args so it won't go to named
-          } else if (positionalArgs[i] !== undefined) {
+          } else if (positionalArgIndex < positionalArgs.length) {
-            this.scope.set(paramName, positionalArgs[i]!)
+            paramValue = positionalArgs[positionalArgIndex]!
+            positionalArgIndex++
+          }
+
+          // If the parameter value is null and a default exists, use the default
+          if (paramValue && paramValue.type === 'null' && fn.defaults[paramName] !== undefined) {
+            const defaultIdx = fn.defaults[paramName]!
+            const defaultValue = this.constants[defaultIdx]!
+            if (defaultValue.type === 'function_def')
+              throw new Error('Default value cannot be a function definition')
+            this.scope.set(paramName, defaultValue)
+          } else if (paramValue) {
+            this.scope.set(paramName, paramValue)
           } else if (fn.defaults[paramName] !== undefined) {
             const defaultIdx = fn.defaults[paramName]!
             const defaultValue = this.constants[defaultIdx]!
@@ -445,7 +742,7 @@ export class VM {
         // Handle variadic parameter (collect remaining positional args)
         if (fn.variadic) {
           const variadicParamName = fn.params[fn.params.length - (fn.named ? 2 : 1)]!
-          const remainingArgs = positionalArgs.slice(fixedParamCount)
+          const remainingArgs = positionalArgs.slice(positionalArgIndex)
           this.scope.set(variadicParamName, { type: 'array', value: remainingArgs })
         }
 
@@ -491,7 +788,7 @@ export class VM {
         const tailFn = this.stack.pop()!
 
         if (tailFn.type !== 'function')
-          throw new Error('TAIL_CALL: not a function')
+          throw new Error(`TAIL_CALL: ${tailFn.value} is not a function`)
 
         this.scope = new Scope(tailFn.parentScope)
 
@@ -500,6 +797,9 @@ export class VM {
         if (tailFn.variadic) tailFixedParamCount--
         if (tailFn.named) tailFixedParamCount--
 
+        // Track which positional args have been consumed
+        let tailPositionalArgIndex = 0
+
         // Bind fixed parameters
         for (let i = 0; i < tailFixedParamCount; i++) {
           const paramName = tailFn.params[i]!
@@ -507,8 +807,9 @@ export class VM {
           if (tailNamedArgs.has(paramName)) {
             this.scope.set(paramName, tailNamedArgs.get(paramName)!)
             tailNamedArgs.delete(paramName)
-          } else if (tailPositionalArgs[i] !== undefined) {
+          } else if (tailPositionalArgIndex < tailPositionalArgs.length) {
-            this.scope.set(paramName, tailPositionalArgs[i]!)
+            this.scope.set(paramName, tailPositionalArgs[tailPositionalArgIndex]!)
+            tailPositionalArgIndex++
           } else if (tailFn.defaults[paramName] !== undefined) {
             const defaultIdx = tailFn.defaults[paramName]!
             const defaultValue = this.constants[defaultIdx]!
@@ -523,7 +824,7 @@ export class VM {
         // Handle variadic parameter
         if (tailFn.variadic) {
           const variadicParamName = tailFn.params[tailFn.params.length - (tailFn.named ? 2 : 1)]!
-          const remainingArgs = tailPositionalArgs.slice(tailFixedParamCount)
+          const remainingArgs = tailPositionalArgs.slice(tailPositionalArgIndex)
           this.scope.set(variadicParamName, { type: 'array', value: remainingArgs })
         }
 
@@ -555,30 +856,8 @@ export class VM {
         this.stack.push(returnValue)
         break
 
-      case OpCode.CALL_NATIVE:
-        const functionName = instruction.operand as string
-        const tsFunction = this.nativeFunctions.get(functionName)
-
-        if (!tsFunction)
-          throw new Error(`CALL_NATIVE: function not found: ${functionName}`)
-
-        // Mark current frame as break target (like CALL does)
-        if (this.callStack.length > 0)
-          this.callStack[this.callStack.length - 1]!.isBreakTarget = true
-
-        // Pop all arguments from stack (TypeScript function consumes entire stack)
-        const tsArgs = [...this.stack]
-        this.stack = []
-
-        // Call the TypeScript function and await if necessary
-        const tsResult = await tsFunction(...tsArgs)
-
-        // Push result back onto stack
-        this.stack.push(tsResult)
-        break
-
       default:
-        throw `Unknown op: ${instruction.op}`
+        throw new Error(`Unknown op: ${instruction.op}`)
     }
   }
 
@@ -595,4 +874,26 @@ export class VM {
     const result = fn(a, b)
     this.stack.push({ type: 'boolean', value: result })
   }
+
+  async callNative(nativeFn: NativeFunction, args: any[]): Promise<Value> {
+    const originalFn = getOriginalFunction(nativeFn)
+
+    const lastArg = args[args.length - 1]
+    if (lastArg && !Array.isArray(lastArg) && typeof lastArg === 'object') {
+      const paramInfo = extractParamInfo(originalFn)
+      const positional = args.slice(0, -1)
+      const named = lastArg
+
+      args = [...positional]
+      for (let i = positional.length; i < paramInfo.params.length; i++) {
+        const paramName = paramInfo.params[i]!
+        if (named[paramName] !== undefined) {
+          args[i] = named[paramName]
+        }
+      }
+    }
+
+    const result = await originalFn.call(this, ...args)
+    return toValue(result, this)
+  }
 }

tests/basic.test.ts

@@ -1,861 +0,0 @@
-import { test, expect } from "bun:test"
-import { run } from "#index"
-import { toBytecode } from "#bytecode"
-
-test("ADD - add two numbers", async () => {
-  const str = `
-  PUSH 1
-  PUSH 5
-  ADD
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 6 })
-
-  const str2 = `
-  PUSH 100
-  PUSH 500
-  ADD
-`
-  expect(await run(toBytecode(str2))).toEqual({ type: 'number', value: 600 })
-})
-
-test("SUB - subtract two numbers", async () => {
-  const str = `
-  PUSH 5
-  PUSH 2
-  SUB
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 3 })
-})
-
-test("MUL - multiply two numbers", async () => {
-  const str = `
-  PUSH 5
-  PUSH 2
-  MUL
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 10 })
-})
-
-test("DIV - divide two numbers", async () => {
-  const str = `
-  PUSH 10
-  PUSH 2
-  DIV
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 5 })
-
-  const str2 = `
-  PUSH 10
-  PUSH 0
-  DIV
-`
-  expect(await run(toBytecode(str2))).toEqual({ type: 'number', value: Infinity })
-})
-
-test("MOD - modulo two numbers", async () => {
-  const str = `
-  PUSH 17
-  PUSH 5
-  MOD
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 2 })
-})
-
-test("PUSH - pushes value onto stack", async () => {
-  const str = `
-  PUSH 42
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 42 })
-})
-
-test("POP - removes top value", async () => {
-  const str = `
-  PUSH 10
-  PUSH 20
-  POP
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 10 })
-})
-
-test("DUP - duplicates top value", async () => {
-  const str = `
-  PUSH 5
-  DUP
-  ADD
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 10 })
-})
-
-test("EQ - equality comparison", async () => {
-  const str = `
-  PUSH 5
-  PUSH 5
-  EQ
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: true })
-
-  const str2 = `
-  PUSH 5
-  PUSH 10
-  EQ
-`
-  expect(await run(toBytecode(str2))).toEqual({ type: 'boolean', value: false })
-})
-
-test("NEQ - not equal comparison", async () => {
-  const str = `
-  PUSH 5
-  PUSH 10
-  NEQ
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: true })
-})
-
-test("LT - less than", async () => {
-  const str = `
-  PUSH 5
-  PUSH 10
-  LT
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: true })
-})
-
-test("GT - greater than", async () => {
-  const str = `
-  PUSH 10
-  PUSH 5
-  GT
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: true })
-})
-
-test("LTE - less than or equal", async () => {
-  // equal case
-  const str = `
-  PUSH 5
-  PUSH 5
-  LTE
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: true })
-
-  // less than case
-  const str2 = `
-  PUSH 3
-  PUSH 5
-  LTE
-`
-  expect(await run(toBytecode(str2))).toEqual({ type: 'boolean', value: true })
-
-  // greater than case (false)
-  const str3 = `
-  PUSH 10
-  PUSH 5
-  LTE
-`
-  expect(await run(toBytecode(str3))).toEqual({ type: 'boolean', value: false })
-})
-
-test("GTE - greater than or equal", async () => {
-  // equal case
-  const str = `
-  PUSH 5
-  PUSH 5
-  GTE
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: true })
-
-  // greater than case
-  const str2 = `
-  PUSH 10
-  PUSH 5
-  GTE
-`
-  expect(await run(toBytecode(str2))).toEqual({ type: 'boolean', value: true })
-
-  // less than case (false)
-  const str3 = `
-  PUSH 3
-  PUSH 5
-  GTE
-`
-  expect(await run(toBytecode(str3))).toEqual({ type: 'boolean', value: false })
-})
-
-test("AND pattern - short circuits when false", async () => {
-  // false && <anything> should short-circuit and return false
-  const str = `
-  PUSH 1
-  PUSH 0
-  EQ
-  DUP
-  JUMP_IF_FALSE .end
-  POP
-  PUSH 999
-  .end:
-`
-  const result = await run(toBytecode(str))
-  expect(result.type).toBe('boolean')
-  if (result.type === 'boolean') {
-    expect(result.value).toBe(false)
-  }
-})
-
-test("AND pattern - evaluates both when true", async () => {
-  const str = `
-  PUSH 1
-  DUP
-  JUMP_IF_FALSE .end
-  POP
-  PUSH 2
-  .end:
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 2 })
-})
-
-test("OR pattern - short circuits when true", async () => {
-  const str = `
-  PUSH 1
-  DUP
-  JUMP_IF_TRUE .end
-  POP
-  PUSH 2
-  .end:
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 1 })
-})
-
-test("OR pattern - evaluates second when false", async () => {
-  const str = `
-  PUSH 1
-  PUSH 0
-  EQ
-  DUP
-  JUMP_IF_TRUE .end
-  POP
-  PUSH 2
-  .end:
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 2 })
-})
-
-test("NOT - logical not", async () => {
-  // number is truthy, so NOT returns false
-  const str = `
-  PUSH 1
-  NOT
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: false })
-
-  // 0 is truthy in this language, so NOT returns false
-  const str2 = `
-  PUSH 0
-  NOT
-`
-  expect(await run(toBytecode(str2))).toEqual({ type: 'boolean', value: false })
-
-  // boolean false is falsy, so NOT returns true
-  const str3 = `
-  PUSH 1
-  PUSH 0
-  EQ
-  NOT
-`
-  expect(await run(toBytecode(str3))).toEqual({ type: 'boolean', value: true })
-})
-
-test("isTruthy - only null and false are falsy", async () => {
-  // 0 is truthy (unlike JS)
-  const str1 = `
-  PUSH 0
-  JUMP_IF_FALSE .end
-  PUSH 1
-  .end:
-`
-  expect(await run(toBytecode(str1))).toEqual({ type: 'number', value: 1 })
-
-  // empty string is truthy (unlike JS)
-  const str2 = `
-  PUSH ''
-  JUMP_IF_FALSE .end
-  PUSH 1
-  .end:
-`
-  expect(await run(toBytecode(str2))).toEqual({ type: 'number', value: 1 })
-
-  // false is falsy
-  const str3 = `
-  PUSH 0
-  PUSH 0
-  EQ
-  JUMP_IF_FALSE .end
-  PUSH 999
-  .end:
-`
-  expect(await run(toBytecode(str3))).toEqual({ type: 'number', value: 999 })
-})
-
-test("HALT - stops execution", async () => {
-  const str = `
-  PUSH 42
-  HALT
-  PUSH 100
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 42 })
-})
-
-test("STORE and LOAD - variables", async () => {
-  const str = `
-  PUSH 42
-  STORE x
-  PUSH 21
-  LOAD x
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 42 })
-})
-
-test("STORE and LOAD - multiple variables", async () => {
-  const str = `
-  PUSH 10
-  STORE a
-  PUSH 20
-  STORE b
-  PUSH 44
-  LOAD a
-  LOAD b
-  ADD
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 30 })
-})
-
-test("TRY_LOAD - variable found", async () => {
-  const str = `
-  PUSH 100
-  STORE count
-  TRY_LOAD count
-  `
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 100 })
-
-  const str2 = `
-  PUSH 'Bobby'
-  STORE name
-  TRY_LOAD name
-  `
-  expect(await run(toBytecode(str2))).toEqual({ type: 'string', value: 'Bobby' })
-})
-
-test("TRY_LOAD - variable missing", async () => {
-  const str = `
-  PUSH 100
-  STORE count
-  TRY_LOAD count1
-  `
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'count1' })
-
-  const str2 = `
-  PUSH 'Bobby'
-  STORE name
-  TRY_LOAD full-name
-  `
-  expect(await run(toBytecode(str2))).toEqual({ type: 'string', value: 'full-name' })
-})
-
-test("TRY_LOAD - with different value types", async () => {
-  // Array
-  const str1 = `
-  PUSH 1
-  PUSH 2
-  PUSH 3
-  MAKE_ARRAY #3
-  STORE arr
-  TRY_LOAD arr
-  `
-  const result1 = await run(toBytecode(str1))
-  expect(result1.type).toBe('array')
-
-  // Dict
-  const str2 = `
-  PUSH 'key'
-  PUSH 'value'
-  MAKE_DICT #1
-  STORE dict
-  TRY_LOAD dict
-  `
-  const result2 = await run(toBytecode(str2))
-  expect(result2.type).toBe('dict')
-
-  // Boolean
-  const str3 = `
-  PUSH true
-  STORE flag
-  TRY_LOAD flag
-  `
-  expect(await run(toBytecode(str3))).toEqual({ type: 'boolean', value: true })
-
-  // Null
-  const str4 = `
-  PUSH null
-  STORE empty
-  TRY_LOAD empty
-  `
-  expect(await run(toBytecode(str4))).toEqual({ type: 'null', value: null })
-})
-
-test("TRY_LOAD - in nested scope", async () => {
-  // Function should be able to TRY_LOAD variable from parent scope
-  const str = `
-  PUSH 42
-  STORE outer
-  MAKE_FUNCTION () .fn
-  PUSH 0
-  PUSH 0
-  CALL
-  HALT
-  .fn:
-  TRY_LOAD outer
-  RETURN
-  `
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 42 })
-})
-
-test("TRY_LOAD - missing variable in nested scope returns name", async () => {
-  // If variable doesn't exist in any scope, should return name as string
-  const str = `
-  PUSH 42
-  STORE outer
-  MAKE_FUNCTION () .fn
-  PUSH 0
-  PUSH 0
-  CALL
-  HALT
-  .fn:
-  TRY_LOAD inner
-  RETURN
-  `
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'inner' })
-})
-
-test("TRY_LOAD - used for conditional variable existence check", async () => {
-  // Pattern: use TRY_LOAD to check if variable exists and get its value or name
-  const str = `
-  PUSH 100
-  STORE count
-  TRY_LOAD count
-  PUSH 'count'
-  EQ
-  `
-  // Variable exists, so TRY_LOAD returns 100, which != 'count'
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: false })
-
-  const str2 = `
-  PUSH 100
-  STORE count
-  TRY_LOAD missing
-  PUSH 'missing'
-  EQ
-  `
-  // Variable missing, so TRY_LOAD returns 'missing', which == 'missing'
-  expect(await run(toBytecode(str2))).toEqual({ type: 'boolean', value: true })
-})
-
-test("TRY_LOAD - with function value", async () => {
-  const str = `
-  MAKE_FUNCTION () .fn
-  STORE myFunc
-  JUMP .skip
-  .fn:
-  PUSH 99
-  RETURN
-  .skip:
-  TRY_LOAD myFunc
-  `
-  const result = await run(toBytecode(str))
-  expect(result.type).toBe('function')
-})
-
-test("JUMP - relative jump forward", async () => {
-  const str = `
-  PUSH 1
-  JUMP .skip
-  PUSH 100
-  .skip:
-  PUSH 2
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 2 })
-})
-
-test("JUMP - forward jump skips instructions", async () => {
-  // Use forward jump to skip, demonstrating relative addressing
-  const str = `
-  PUSH 100
-  JUMP .end
-  PUSH 200
-  PUSH 300
-  .end:
-  PUSH 400
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 400 })
-})
-
-test("JUMP_IF_FALSE - conditional jump when false", async () => {
-  const str = `
-  PUSH 1
-  PUSH 0
-  EQ
-  JUMP_IF_FALSE .skip
-  PUSH 100
-  .skip:
-  PUSH 42
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 42 })
-})
-
-test("JUMP_IF_FALSE - no jump when true", async () => {
-  const str = `
-  PUSH 1
-  JUMP_IF_FALSE .skip
-  PUSH 100
-  .skip:
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 100 })
-})
-
-test("JUMP_IF_TRUE - conditional jump when true", async () => {
-  const str = `
-  PUSH 1
-  JUMP_IF_TRUE .skip
-  PUSH 100
-  .skip:
-  PUSH 42
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 42 })
-})
-
-test("MAKE_ARRAY - creates array", async () => {
-  const str = `
-  PUSH 10
-  PUSH 20
-  PUSH 30
-  MAKE_ARRAY #3
-`
-  const result = await run(toBytecode(str))
-  expect(result.type).toBe('array')
-  if (result.type === 'array') {
-    expect(result.value).toHaveLength(3)
-    expect(result.value[0]).toEqual({ type: 'number', value: 10 })
-    expect(result.value[1]).toEqual({ type: 'number', value: 20 })
-    expect(result.value[2]).toEqual({ type: 'number', value: 30 })
-  }
-})
-
-test("ARRAY_GET - gets element", async () => {
-  const str = `
-  PUSH 10
-  PUSH 20
-  PUSH 30
-  MAKE_ARRAY #3
-  PUSH 1
-  ARRAY_GET
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 20 })
-})
-
-test("ARRAY_SET - sets element", async () => {
-  const str = `
-  PUSH 10
-  PUSH 20
-  PUSH 30
-  MAKE_ARRAY #3
-  DUP
-  PUSH 1
-  PUSH 99
-  ARRAY_SET
-  PUSH 1
-  ARRAY_GET
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 99 })
-})
-
-test("ARRAY_PUSH - appends to array", async () => {
-  const str = `
-  PUSH 10
-  PUSH 20
-  MAKE_ARRAY #2
-  DUP
-  PUSH 30
-  ARRAY_PUSH
-  ARRAY_LEN
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 3 })
-})
-
-test("ARRAY_PUSH - mutates original array", async () => {
-  const str = `
-  PUSH 10
-  PUSH 20
-  MAKE_ARRAY #2
-  DUP
-  PUSH 30
-  ARRAY_PUSH
-  PUSH 2
-  ARRAY_GET
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 30 })
-})
-
-test("ARRAY_LEN - gets length", async () => {
-  const str = `
-  PUSH 10
-  PUSH 20
-  PUSH 30
-  MAKE_ARRAY #3
-  ARRAY_LEN
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 3 })
-})
-
-test("MAKE_DICT - creates dict", async () => {
-  const str = `
-  PUSH 'name'
-  PUSH 'Alice'
-  PUSH 'age'
-  PUSH 30
-  MAKE_DICT #2
-`
-  const result = await run(toBytecode(str))
-  expect(result.type).toBe('dict')
-  if (result.type === 'dict') {
-    expect(result.value.size).toBe(2)
-    expect(result.value.get('name')).toEqual({ type: 'string', value: 'Alice' })
-    expect(result.value.get('age')).toEqual({ type: 'number', value: 30 })
-  }
-})
-
-test("DICT_GET - gets value", async () => {
-  const str = `
-  PUSH 'name'
-  PUSH 'Bob'
-  MAKE_DICT #1
-  PUSH 'name'
-  DICT_GET
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'Bob' })
-})
-
-test("DICT_SET - sets value", async () => {
-  const str = `
-  MAKE_DICT #0
-  DUP
-  PUSH 'key'
-  PUSH 'value'
-  DICT_SET
-  PUSH 'key'
-  DICT_GET
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'value' })
-})
-
-test("DICT_HAS - checks key exists", async () => {
-  const str = `
-  PUSH 'key'
-  PUSH 'value'
-  MAKE_DICT #1
-  PUSH 'key'
-  DICT_HAS
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: true })
-})
-
-test("DICT_HAS - checks key missing", async () => {
-  const str = `
-  MAKE_DICT #0
-  PUSH 'missing'
-  DICT_HAS
-`
-  expect(await run(toBytecode(str))).toEqual({ type: 'boolean', value: false })
-})
-
-test("BREAK - throws error when no break target", async () => {
-  // BREAK requires a break target frame on the call stack
-  // A single function call has no previous frame to mark as break target
-  const bytecode = toBytecode(`
-    MAKE_FUNCTION () .fn
-    PUSH 0
-    PUSH 0
-    CALL
-    HALT
-    .fn:
-    BREAK
-  `)
-
-  try {
-    await run(bytecode)
-    expect(true).toBe(false)  // Should not reach here
-  } catch (e: any) {
-    expect(e.message).toContain('no break target found')
-  }
-})
-
-test("BREAK - exits from nested function call", async () => {
-  // BREAK unwinds to the break target (the outer function's frame)
-  // Main calls outer, outer calls inner, inner BREAKs back to outer's caller (main)
-  const bytecode = toBytecode(`
-    MAKE_FUNCTION () .outer
-    PUSH 0
-    PUSH 0
-    CALL
-    PUSH 42
-    HALT
-    .outer:
-    MAKE_FUNCTION () .inner
-    PUSH 0
-    PUSH 0
-    CALL
-    PUSH 99
-    RETURN
-    .inner:
-    BREAK
-  `)
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 42 })
-})
-
-test("JUMP backward - simple loop", async () => {
-  // Very simple: counter starts at 0, loops 3 times incrementing
-  // On 3rd iteration (counter==3), exits and returns counter
-  const bytecode = toBytecode(`
-    PUSH 0
-    STORE counter
-    .loop:
-    LOAD counter
-    PUSH 3
-    EQ
-    JUMP_IF_FALSE .body
-    LOAD counter
-    HALT
-    .body:
-    LOAD counter
-    PUSH 1
-    ADD
-    STORE counter
-    JUMP .loop
-  `)
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 3 })
-})
-
-test("emoji variable names - string format", async () => {
-  const bytecode = toBytecode(`
-    PUSH 5
-    STORE 💎
-    LOAD 💎
-    HALT
-  `)
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 5 })
-})
-
-test("emoji variable names - array format", async () => {
-  const bytecode = toBytecode([
-    ["PUSH", 100],
-    ["STORE", "💰"],
-    ["LOAD", "💰"],
-    ["PUSH", 50],
-    ["ADD"],
-    ["HALT"]
-  ])
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 150 })
-})
-
-test("unicode variable names - Japanese", async () => {
-  const bytecode = toBytecode(`
-    PUSH 42
-    STORE 変数
-    LOAD 変数
-    HALT
-  `)
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 42 })
-})
-
-test("unicode variable names - Chinese", async () => {
-  const bytecode = toBytecode([
-    ["PUSH", 888],
-    ["STORE", "数字"],
-    ["LOAD", "数字"],
-    ["HALT"]
-  ])
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 888 })
-})
-
-test("emoji in function parameters", async () => {
-  const bytecode = toBytecode(`
-    MAKE_FUNCTION (💎 🌟) .add
-    STORE add
-    JUMP .after
-    .add:
-    LOAD 💎
-    LOAD 🌟
-    ADD
-    RETURN
-    .after:
-    LOAD add
-    PUSH 10
-    PUSH 20
-    PUSH 2
-    PUSH 0
-    CALL
-    HALT
-  `)
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 30 })
-})
-
-test("emoji with defaults and variadic", async () => {
-  const bytecode = toBytecode([
-    ["MAKE_FUNCTION", ["🎯=100", "...🎨"], ".fn"],
-    ["STORE", "fn"],
-    ["JUMP", ".after"],
-    [".fn:"],
-    ["LOAD", "🎯"],
-    ["RETURN"],
-    [".after:"],
-    ["LOAD", "fn"],
-    ["PUSH", 0],
-    ["PUSH", 0],
-    ["CALL"],
-    ["HALT"]
-  ])
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 100 })
-})
-
-test("mixed emoji and regular names", async () => {
-  const bytecode = toBytecode([
-    ["PUSH", 10],
-    ["STORE", "💎"],
-    ["PUSH", 20],
-    ["STORE", "value"],
-    ["PUSH", 30],
-    ["STORE", "🌟"],
-    ["LOAD", "💎"],
-    ["LOAD", "value"],
-    ["ADD"],
-    ["LOAD", "🌟"],
-    ["ADD"],
-    ["HALT"]
-  ])
-
-  const result = await run(bytecode)
-  expect(result).toEqual({ type: 'number', value: 60 })
-})
-

tests/bitwise.test.ts

@@ -0,0 +1,107 @@
+import { expect, describe, test } from 'bun:test'
+import { toBytecode, run } from '#reef'
+
+describe('bitwise operations', () => {
+  test('BIT_AND', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 3], ["BIT_AND"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(1)
+  })
+
+  test('BIT_AND with zero', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 0], ["BIT_AND"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(0)
+  })
+
+  test('BIT_OR', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 3], ["BIT_OR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(7)
+  })
+
+  test('BIT_OR with zero', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 0], ["BIT_OR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(5)
+  })
+
+  test('BIT_XOR', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 3], ["BIT_XOR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(6)
+  })
+
+  test('BIT_XOR with itself returns zero', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 5], ["BIT_XOR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(0)
+  })
+
+  test('BIT_SHL', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 2], ["BIT_SHL"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(20)
+  })
+
+  test('BIT_SHL by zero', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 5], ["PUSH", 0], ["BIT_SHL"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(5)
+  })
+
+  test('BIT_SHR', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 20], ["PUSH", 2], ["BIT_SHR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(5)
+  })
+
+  test('BIT_SHR preserves sign for negative numbers', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", -20], ["PUSH", 2], ["BIT_SHR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(-5)
+  })
+
+  test('BIT_USHR', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", -1], ["PUSH", 1], ["BIT_USHR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(2147483647)
+  })
+
+  test('BIT_USHR does not preserve sign', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", -8], ["PUSH", 1], ["BIT_USHR"], ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(2147483644)
+  })
+
+  test('compound bitwise operations', async () => {
+    const bytecode = toBytecode([
+      // (5 & 3) | (8 ^ 12)
+      ["PUSH", 5], ["PUSH", 3], ["BIT_AND"],    // stack: [1]
+      ["PUSH", 8], ["PUSH", 12], ["BIT_XOR"],   // stack: [1, 4]
+      ["BIT_OR"],                                // stack: [5]
+      ["HALT"]
+    ])
+    await expect(bytecode).toBeNumber(5)
+  })
+
+  test('shift with large shift amounts', async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 1], ["PUSH", 31], ["BIT_SHL"], ["HALT"]
+    ])
+    // 1 << 31 = -2147483648 (most significant bit set)
+    await expect(bytecode).toBeNumber(-2147483648)
+  })
+})

tests/exceptions.test.ts

@@ -15,7 +15,7 @@ test("PUSH_TRY and POP_TRY - no exception thrown", async () => {
     PUSH 999
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 52 })
+  await expect(str).toBeNumber(52)
 })
 
 test("THROW - catch exception with error value", async () => {
@@ -29,7 +29,7 @@ test("THROW - catch exception with error value", async () => {
     .catch:
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'error occurred' })
+  await expect(str).toBeString('error occurred')
 })
 
 test("THROW - uncaught exception throws JS error", async () => {
@@ -58,7 +58,7 @@ test("THROW - exception with nested try blocks", async () => {
     PUSH "outer error"
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'inner error' })
+  await expect(str).toBeString('inner error')
 })
 
 test("THROW - exception skips outer handler", async () => {
@@ -75,7 +75,7 @@ test("THROW - exception skips outer handler", async () => {
     .outer_catch:
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'error message' })
+  await expect(str).toBeString('error message')
 })
 
 test("THROW - exception unwinds call stack", async () => {
@@ -150,7 +150,7 @@ test("PUSH_FINALLY - finally executes after successful try", async () => {
     ADD
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 110 })
+  await expect(str).toBeNumber(110)
 })
 
 test("PUSH_FINALLY - finally executes after exception", async () => {
@@ -169,7 +169,7 @@ test("PUSH_FINALLY - finally executes after exception", async () => {
     PUSH "finally ran"
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'string', value: 'finally ran' })
+  await expect(str).toBeString('finally ran')
 })
 
 test("PUSH_FINALLY - finally without catch", async () => {
@@ -189,7 +189,7 @@ test("PUSH_FINALLY - finally without catch", async () => {
     ADD
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 52 })
+  await expect(str).toBeNumber(52)
 })
 
 test("PUSH_FINALLY - nested try-finally blocks", async () => {
@@ -214,7 +214,7 @@ test("PUSH_FINALLY - nested try-finally blocks", async () => {
     ADD
     HALT
   `
-  expect(await run(toBytecode(str))).toEqual({ type: 'number', value: 11 })
+  await expect(str).toBeNumber(11)
 })
 
 test("PUSH_FINALLY - error when no handler", async () => {

tests/functions-parameter.test.ts

@@ -0,0 +1,232 @@
+import { test, expect, describe } from "bun:test"
+import { run, VM } from "#index"
+import { toBytecode } from "#bytecode"
+
+describe("functions parameter", () => {
+  test("pass functions to run()", async () => {
+    const bytecode = toBytecode(`
+      LOAD add
+      PUSH 5
+      PUSH 3
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const result = await run(bytecode, {
+      add: (a: number, b: number) => a + b
+    })
+
+    expect(result).toEqual({ type: 'number', value: 8 })
+  })
+
+  test("pass functions to VM constructor", async () => {
+    const bytecode = toBytecode(`
+      LOAD multiply
+      PUSH 10
+      PUSH 2
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const vm = new VM(bytecode, {
+      multiply: (a: number, b: number) => a * b
+    })
+
+    const result = await vm.run()
+    expect(result).toEqual({ type: 'number', value: 20 })
+  })
+
+  test("pass multiple functions", async () => {
+    const bytecode = toBytecode(`
+      LOAD add
+      PUSH 10
+      PUSH 5
+      PUSH 2
+      PUSH 0
+      CALL
+      STORE sum
+      LOAD multiply
+      LOAD sum
+      PUSH 3
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const result = await run(bytecode, {
+      add: (a: number, b: number) => a + b,
+      multiply: (a: number, b: number) => a * b
+    })
+
+    expect(result).toEqual({ type: 'number', value: 45 })
+  })
+
+  test("auto-wraps native functions", async () => {
+    const bytecode = toBytecode(`
+      LOAD concat
+      PUSH "hello"
+      PUSH "world"
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const result = await run(bytecode, {
+      concat: (a: string, b: string) => a + " " + b
+    })
+
+    expect(result).toEqual({ type: 'string', value: 'hello world' })
+  })
+
+  test("works with async functions", async () => {
+    const bytecode = toBytecode(`
+      LOAD delay
+      PUSH 100
+      PUSH 1
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const result = await run(bytecode, {
+      delay: async (n: number) => {
+        await new Promise(resolve => setTimeout(resolve, 1))
+        return n * 2
+      }
+    })
+
+    expect(result).toEqual({ type: 'number', value: 200 })
+  })
+
+  test("can combine with manual vm.set", async () => {
+    const bytecode = toBytecode(`
+      LOAD add
+      PUSH 5
+      PUSH 3
+      PUSH 2
+      PUSH 0
+      CALL
+      STORE sum
+      LOAD subtract
+      LOAD sum
+      PUSH 2
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const vm = new VM(bytecode, {
+      add: (a: number, b: number) => a + b
+    })
+
+    // Register another function manually
+    vm.set('subtract', (a: number, b: number) => a - b)
+
+    const result = await vm.run()
+    expect(result).toEqual({ type: 'number', value: 6 })
+  })
+
+  test("no functions parameter (undefined)", async () => {
+    const bytecode = toBytecode(`
+      PUSH 42
+      HALT
+    `)
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 42 })
+  })
+
+  test("empty functions object", async () => {
+    const bytecode = toBytecode(`
+      PUSH 99
+      HALT
+    `)
+
+    const result = await run(bytecode, {})
+    expect(result).toEqual({ type: 'number', value: 99 })
+  })
+
+  test("function throws error", async () => {
+    const bytecode = toBytecode(`
+      LOAD divide
+      PUSH 0
+      PUSH 1
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    try {
+      await run(bytecode, {
+        divide: (n: number) => {
+          if (n === 0) throw new Error("Cannot divide by zero")
+          return 100 / n
+        }
+      })
+      expect(true).toBe(false) // Should not reach here
+    } catch (e: any) {
+      expect(e.message).toContain("Cannot divide by zero")
+    }
+  })
+
+  test("complex workflow with multiple function calls", async () => {
+    const bytecode = toBytecode(`
+      LOAD add
+      PUSH 5
+      PUSH 3
+      PUSH 2
+      PUSH 0
+      CALL
+      STORE result
+      LOAD multiply
+      LOAD result
+      PUSH 2
+      PUSH 2
+      PUSH 0
+      CALL
+      STORE final
+      LOAD format
+      LOAD final
+      PUSH 1
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const result = await run(bytecode, {
+      add: (a: number, b: number) => a + b,
+      multiply: (a: number, b: number) => a * b,
+      format: (n: number) => `Result: ${n}`
+    })
+
+    expect(result).toEqual({ type: 'string', value: 'Result: 16' })
+  })
+
+  test("function overriding - later registration wins", async () => {
+    const bytecode = toBytecode(`
+      LOAD getValue
+      PUSH 5
+      PUSH 1
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const vm = new VM(bytecode, {
+      getValue: () => 100
+    })
+
+    // Override with manual registration
+    vm.set('getValue', () => 200)
+
+    const result = await vm.run()
+    expect(result).toEqual({ type: 'number', value: 200 })
+  })
+})

tests/functions.test.ts

@@ -1,13 +1,13 @@
 import { test, expect } from "bun:test"
 import { toBytecode } from "#bytecode"
-import { VM } from "#vm"
+import { toValue, run } from "#reef"
 
 test("MAKE_FUNCTION - creates function with captured scope", async () => {
   const bytecode = toBytecode(`
     MAKE_FUNCTION () #999
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result.type).toBe('function')
   if (result.type === 'function') {
     expect(result.body).toBe(999)
@@ -26,7 +26,7 @@ test("CALL and RETURN - basic function call", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'number', value: 42 })
 })
 
@@ -42,7 +42,7 @@ test("CALL and RETURN - function with one parameter", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'number', value: 100 })
 })
 
@@ -61,7 +61,7 @@ test("CALL and RETURN - function with two parameters", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'number', value: 30 })
 })
 
@@ -79,7 +79,7 @@ test("CALL - variadic function with no fixed params", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({
     type: 'array',
     value: [
@@ -104,7 +104,7 @@ test("CALL - variadic function with one fixed param", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // x should be 10, rest should be [20, 30]
   expect(result).toEqual({
     type: 'array',
@@ -130,7 +130,7 @@ test("CALL - variadic function with two fixed params", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // a=1, b=2, rest=[3, 4]
   expect(result).toEqual({
     type: 'array',
@@ -153,7 +153,7 @@ test("CALL - variadic function with no extra args", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // rest should be empty array
   expect(result).toEqual({ type: 'array', value: [] })
 })
@@ -169,7 +169,7 @@ test("CALL - variadic function with defaults on fixed params", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // x should use default value 5
   expect(result).toEqual({ type: 'number', value: 5 })
 })
@@ -188,7 +188,7 @@ test("TAIL_CALL - variadic function", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // Should return the rest array [2, 3]
   expect(result).toEqual({
     type: 'array',
@@ -214,7 +214,7 @@ test("CALL - named args function with no fixed params", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result.type).toBe('dict')
   if (result.type === 'dict') {
     expect(result.value.get('name')).toEqual({ type: 'string', value: 'Bob' })
@@ -236,7 +236,7 @@ test("CALL - named args function with one fixed param", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result.type).toBe('dict')
   if (result.type === 'dict') {
     expect(result.value.get('name')).toEqual({ type: 'string', value: 'Alice' })
@@ -258,7 +258,7 @@ test("CALL - named args with matching param name should bind to param not named"
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // name should be bound as regular param, not collected in named
   expect(result).toEqual({ type: 'string', value: 'Bob' })
 })
@@ -278,7 +278,7 @@ test("CALL - named args that match param names should not be in named", async ()
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result.type).toBe('dict')
   if (result.type === 'dict') {
     // Only city should be in named, name should be bound to param
@@ -304,7 +304,7 @@ test("CALL - mixed variadic and named args", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // rest should have [2, 3]
   expect(result).toEqual({
     type: 'array',
@@ -331,7 +331,7 @@ test("CALL - mixed variadic and named args, check named", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result.type).toBe('dict')
   if (result.type === 'dict') {
     expect(result.value.get('name')).toEqual({ type: 'string', value: 'Bob' })
@@ -350,7 +350,7 @@ test("CALL - named args with no extra named args", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // named should be empty dict
   expect(result.type).toBe('dict')
   if (result.type === 'dict') {
@@ -371,11 +371,34 @@ test("CALL - named args with defaults on fixed params", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   // x should use default value 5
   expect(result).toEqual({ type: 'number', value: 5 })
 })
 
+test("CALL - fixed params can be named", async () => {
+  const bytecode = toBytecode(`
+    MAKE_FUNCTION (a b) .func_0
+    STORE minus
+    TRY_LOAD minus
+    PUSH 200
+    PUSH 'a'
+    PUSH 900
+    PUSH 1
+    PUSH 1
+    CALL
+    HALT
+    .func_0:
+    TRY_LOAD a
+    TRY_LOAD b
+    SUB
+    RETURN
+  `)
+
+  const result = await run(bytecode)
+  expect(result).toEqual(toValue(700))
+})
+
 test("TRY_CALL - calls function if found", async () => {
   const bytecode = toBytecode([
     ["MAKE_FUNCTION", [], ".body"],
@@ -387,7 +410,7 @@ test("TRY_CALL - calls function if found", async () => {
     ["RETURN"]
   ])
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'number', value: 42 })
 })
 
@@ -399,7 +422,7 @@ test("TRY_CALL - pushes value if variable exists but is not a function", async (
     ["HALT"]
   ])
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'number', value: 99 })
 })
 
@@ -409,7 +432,7 @@ test("TRY_CALL - pushes string if variable not found", async () => {
     ["HALT"]
   ])
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'string', value: 'unknownVar' })
 })
 
@@ -423,7 +446,7 @@ test("TRY_CALL - handles arrays", async () => {
     ["HALT"]
   ])
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result.type).toBe('array')
   if (result.type === 'array') {
     expect(result.value).toEqual([
@@ -443,7 +466,7 @@ test("TRY_CALL - handles dicts", async () => {
     ["HALT"]
   ])
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result.type).toBe('dict')
   if (result.type === 'dict') {
     expect(result.value.get('key')).toEqual({ type: 'string', value: 'value' })
@@ -458,13 +481,13 @@ test("TRY_CALL - handles null values", async () => {
     ["HALT"]
   ])
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'null', value: null })
 })
 
 test("TRY_CALL - function can access its parameters", async () => {
   const bytecode = toBytecode([
-    ["MAKE_FUNCTION", ["x"], ".body"],
+    ["MAKE_FUNCTION", ["x=0"], ".body"],
     ["STORE", "addFive"],
     ["PUSH", 10],
     ["STORE", "x"],
@@ -477,9 +500,9 @@ test("TRY_CALL - function can access its parameters", async () => {
     ["RETURN"]
   ])
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
-  // Function is called with 0 args, so x inside function should be null
+  // Function is called with 0 args, so x defaults to 0
-  // Then we add 5 to null (which coerces to 0)
+  // Then we add 5 to 0
   expect(result).toEqual({ type: 'number', value: 5 })
 })
 
@@ -493,6 +516,209 @@ test("TRY_CALL - with string format", async () => {
     RETURN
   `)
 
-  const result = await new VM(bytecode).run()
+  const result = await run(bytecode)
   expect(result).toEqual({ type: 'number', value: 100 })
 })
+
+test("CALL - passing null triggers default value for single parameter", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["x=42"], ".body"],
+    ["STORE", "func"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "func"],
+    ["PUSH", null],
+    ["PUSH", 1],
+    ["PUSH", 0],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // Passing null should trigger the default value of 42
+  expect(result).toEqual({ type: 'number', value: 42 })
+})
+
+test("CALL - passing null triggers default value for multiple parameters", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["a=10", "b=20", "c=30"], ".body"],
+    ["STORE", "func"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "a"],
+    ["LOAD", "b"],
+    ["ADD"],
+    ["LOAD", "c"],
+    ["ADD"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "func"],
+    ["PUSH", 5],
+    ["PUSH", null],
+    ["PUSH", null],
+    ["PUSH", 3],
+    ["PUSH", 0],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // a=5 (provided), b=20 (null triggers default), c=30 (null triggers default)
+  // Result: 5 + 20 + 30 = 55
+  expect(result).toEqual({ type: 'number', value: 55 })
+})
+
+test("CALL - null in middle parameter triggers default", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["x=100", "y=200", "z=300"], ".body"],
+    ["STORE", "func"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["LOAD", "y"],
+    ["ADD"],
+    ["LOAD", "z"],
+    ["ADD"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "func"],
+    ["PUSH", 1],
+    ["PUSH", null],
+    ["PUSH", 3],
+    ["PUSH", 3],
+    ["PUSH", 0],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // x=1, y=200 (null triggers default), z=3
+  // Result: 1 + 200 + 3 = 204
+  expect(result).toEqual({ type: 'number', value: 204 })
+})
+
+test("CALL - null with named arguments triggers default", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["x=50", "y=75"], ".body"],
+    ["STORE", "func"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["LOAD", "y"],
+    ["ADD"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "func"],
+    ["PUSH", "x"],
+    ["PUSH", null],
+    ["PUSH", "y"],
+    ["PUSH", 25],
+    ["PUSH", 0],
+    ["PUSH", 2],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // x=50 (null triggers default), y=25 (provided via named arg)
+  // Result: 50 + 25 = 75
+  expect(result).toEqual({ type: 'number', value: 75 })
+})
+
+test("CALL - null with string default value", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["name='Guest'"], ".body"],
+    ["STORE", "greet"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["PUSH", "Hello, "],
+    ["LOAD", "name"],
+    ["ADD"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "greet"],
+    ["PUSH", null],
+    ["PUSH", 1],
+    ["PUSH", 0],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // Passing null should trigger the default value 'Guest'
+  expect(result).toEqual({ type: 'string', value: 'Hello, Guest' })
+})
+
+test("CALL - null with no default still results in null", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["x"], ".body"],
+    ["STORE", "func"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "func"],
+    ["PUSH", null],
+    ["PUSH", 1],
+    ["PUSH", 0],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // No default value, so null should be returned
+  expect(result).toEqual({ type: 'null', value: null })
+})
+
+test("CALL - null triggers default with variadic parameters", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["x=99", "...rest"], ".body"],
+    ["STORE", "func"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "func"],
+    ["PUSH", null],
+    ["PUSH", 1],
+    ["PUSH", 2],
+    ["PUSH", 3],
+    ["PUSH", 4],
+    ["PUSH", 0],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // x should be 99 (null triggers default), rest gets [1, 2, 3]
+  expect(result).toEqual({ type: 'number', value: 99 })
+})
+
+test("CALL - null triggers default with @named parameter", async () => {
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["x=777", "@named"], ".body"],
+    ["STORE", "func"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["RETURN"],
+    [".end:"],
+    ["LOAD", "func"],
+    ["PUSH", null],
+    ["PUSH", "foo"],
+    ["PUSH", "bar"],
+    ["PUSH", 1],
+    ["PUSH", 1],
+    ["CALL"],
+    ["HALT"]
+  ])
+
+  const result = await run(bytecode)
+  // x should be 777 (null triggers default)
+  expect(result).toEqual({ type: 'number', value: 777 })
+})

tests/regex.test.ts

@@ -0,0 +1,459 @@
+import { test, expect, describe } from "bun:test"
+import { run } from "#index"
+import { toBytecode } from "#bytecode"
+
+describe("RegExp", () => {
+  test("basic pattern parsing", async () => {
+    const str = `
+    PUSH /hello/
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('hello')
+      expect(result.value.flags).toBe('')
+    }
+  })
+
+  test("pattern with flags", async () => {
+    const str = `
+    PUSH /test/gi
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('test')
+      expect(result.value.global).toBe(true)
+      expect(result.value.ignoreCase).toBe(true)
+    }
+  })
+
+  test("multiple flag combinations", async () => {
+    // Test i flag
+    const str1 = `
+    PUSH /pattern/i
+    `
+    const result1 = await run(toBytecode(str1))
+    expect(result1.type).toBe('regex')
+    if (result1.type === 'regex') {
+      expect(result1.value.ignoreCase).toBe(true)
+    }
+
+    // Test g flag
+    const str2 = `
+    PUSH /pattern/g
+    `
+    const result2 = await run(toBytecode(str2))
+    expect(result2.type).toBe('regex')
+    if (result2.type === 'regex') {
+      expect(result2.value.global).toBe(true)
+    }
+
+    // Test m flag
+    const str3 = `
+    PUSH /pattern/m
+    `
+    const result3 = await run(toBytecode(str3))
+    expect(result3.type).toBe('regex')
+    if (result3.type === 'regex') {
+      expect(result3.value.multiline).toBe(true)
+    }
+
+    // Test combined flags
+    const str4 = `
+    PUSH /pattern/gim
+    `
+    const result4 = await run(toBytecode(str4))
+    expect(result4.type).toBe('regex')
+    if (result4.type === 'regex') {
+      expect(result4.value.global).toBe(true)
+      expect(result4.value.ignoreCase).toBe(true)
+      expect(result4.value.multiline).toBe(true)
+    }
+  })
+
+  test("complex patterns", async () => {
+    // Character class
+    const str1 = `
+    PUSH /[a-z0-9]+/
+    `
+    const result1 = await run(toBytecode(str1))
+    expect(result1.type).toBe('regex')
+    if (result1.type === 'regex') {
+      expect(result1.value.source).toBe('[a-z0-9]+')
+    }
+
+    // Quantifiers
+    const str2 = `
+    PUSH /a{2,4}/
+    `
+    const result2 = await run(toBytecode(str2))
+    expect(result2.type).toBe('regex')
+    if (result2.type === 'regex') {
+      expect(result2.value.source).toBe('a{2,4}')
+    }
+
+    // Groups and alternation
+    const str3 = `
+    PUSH /(foo|bar)/
+    `
+    const result3 = await run(toBytecode(str3))
+    expect(result3.type).toBe('regex')
+    if (result3.type === 'regex') {
+      expect(result3.value.source).toBe('(foo|bar)')
+    }
+
+    // Anchors and special chars
+    const str4 = `
+    PUSH /^[a-z]+$/
+    `
+    const result4 = await run(toBytecode(str4))
+    expect(result4.type).toBe('regex')
+    if (result4.type === 'regex') {
+      expect(result4.value.source).toBe('^[a-z]+$')
+    }
+  })
+
+  test("escaping special characters", async () => {
+    const str = `
+    PUSH /\\d+\\.\\d+/
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('\\d+\\.\\d+')
+    }
+  })
+
+  test("store and load", async () => {
+    const str = `
+    PUSH /test/i
+    STORE pattern
+    LOAD pattern
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('test')
+      expect(result.value.ignoreCase).toBe(true)
+    }
+  })
+
+  test("TRY_LOAD with regex", async () => {
+    const str = `
+    PUSH /hello/g
+    STORE regex
+    TRY_LOAD regex
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('hello')
+      expect(result.value.global).toBe(true)
+    }
+  })
+
+  test("NEQ comparison", async () => {
+    const str = `
+    PUSH /foo/
+    PUSH /bar/
+    NEQ
+    `
+    await expect(str).toBeBoolean(true)
+
+    const str2 = `
+    PUSH /test/i
+    PUSH /test/i
+    NEQ
+    `
+    await expect(str2).toBeBoolean(false)
+  })
+
+  test("is truthy", async () => {
+    // Regex values should be truthy (not null or false)
+    const str = `
+    PUSH /test/
+    JUMP_IF_FALSE .end
+    PUSH 42
+    .end:
+    `
+    await expect(str).toBeNumber(42)
+  })
+
+  test("NOT returns false (regex is truthy)", async () => {
+    const str = `
+    PUSH /pattern/
+    NOT
+    `
+    await expect(str).toBeBoolean(false)
+  })
+
+  test("in arrays", async () => {
+    const str = `
+    PUSH /first/
+    PUSH /second/i
+    PUSH /third/g
+    MAKE_ARRAY #3
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('array')
+    if (result.type === 'array') {
+      expect(result.value).toHaveLength(3)
+
+      expect(result.value[0]!.type).toBe('regex')
+      if (result.value[0]!.type === 'regex') {
+        expect(result.value[0]!.value.source).toBe('first')
+      }
+
+      expect(result.value[1]!.type).toBe('regex')
+      if (result.value[1]!.type === 'regex') {
+        expect(result.value[1]!.value.source).toBe('second')
+        expect(result.value[1]!.value.ignoreCase).toBe(true)
+      }
+
+      expect(result.value[2]!.type).toBe('regex')
+      if (result.value[2]!.type === 'regex') {
+        expect(result.value[2]!.value.source).toBe('third')
+        expect(result.value[2]!.value.global).toBe(true)
+      }
+    }
+  })
+
+  test("retrieve from array", async () => {
+    const str = `
+    PUSH /pattern/i
+    PUSH /test/g
+    MAKE_ARRAY #2
+    PUSH 1
+    ARRAY_GET
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('test')
+      expect(result.value.global).toBe(true)
+    }
+  })
+
+  test("in dicts", async () => {
+    const str = `
+    PUSH 'email'
+    PUSH /^[a-z@.]+$/i
+    PUSH 'phone'
+    PUSH /\\d{3}-\\d{4}/
+    MAKE_DICT #2
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('dict')
+    if (result.type === 'dict') {
+      expect(result.value.size).toBe(2)
+
+      const email = result.value.get('email')
+      expect(email?.type).toBe('regex')
+      if (email?.type === 'regex') {
+        expect(email.value.source).toBe('^[a-z@.]+$')
+        expect(email.value.ignoreCase).toBe(true)
+      }
+
+      const phone = result.value.get('phone')
+      expect(phone?.type).toBe('regex')
+      if (phone?.type === 'regex') {
+        expect(phone.value.source).toBe('\\d{3}-\\d{4}')
+      }
+    }
+  })
+
+  test("retrieve from dict", async () => {
+    const str = `
+    PUSH 'pattern'
+    PUSH /test/gim
+    MAKE_DICT #1
+    PUSH 'pattern'
+    DICT_GET
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('test')
+      expect(result.value.global).toBe(true)
+      expect(result.value.ignoreCase).toBe(true)
+      expect(result.value.multiline).toBe(true)
+    }
+  })
+
+  test("with STR_CONCAT converts to string", async () => {
+    const str = `
+    PUSH "Pattern: "
+    PUSH /test/gi
+    STR_CONCAT #2
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('string')
+    if (result.type === 'string') {
+      expect(result.value).toBe('Pattern: /test/gi')
+    }
+  })
+
+  test("multiple regex in STR_CONCAT", async () => {
+    const str = `
+    PUSH /foo/
+    PUSH " and "
+    PUSH /bar/i
+    STR_CONCAT #3
+    `
+    await expect(str).toBeString('/foo/ and /bar/i')
+  })
+
+  test("DUP with regex", async () => {
+    const str = `
+    PUSH /pattern/i
+    DUP
+    EQ
+    `
+    // Same regex duplicated should be equal
+    await expect(str).toBeBoolean(true)
+  })
+
+  test("empty pattern", async () => {
+    const str = `
+    PUSH //
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('(?:)')
+    }
+  })
+
+  test("pattern with forward slashes escaped", async () => {
+    const str = `
+    PUSH /https:\\/\\//
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('https:\\/\\/')
+    }
+  })
+
+  test("unicode patterns", async () => {
+    const str = `
+    PUSH /こんにちは/
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('こんにちは')
+    }
+  })
+
+  test("emoji in pattern", async () => {
+    const str = `
+    PUSH /🎉+/
+    `
+    const result = await run(toBytecode(str))
+    expect(result.type).toBe('regex')
+    if (result.type === 'regex') {
+      expect(result.value.source).toBe('🎉+')
+    }
+  })
+
+  test("comparing different regex types", async () => {
+    // Different patterns
+    const str1 = `
+    PUSH /abc/
+    PUSH /xyz/
+    EQ
+    `
+    await expect(str1).toBeBoolean(false)
+
+    // Same pattern, different flags
+    const str2 = `
+    PUSH /test/
+    PUSH /test/i
+    EQ
+    `
+    await expect(str2).toBeBoolean(false)
+
+    // Different order of flags (should be equal)
+    const str3 = `
+    PUSH /test/ig
+    PUSH /test/gi
+    EQ
+    `
+    await expect(str3).toBeBoolean(true)
+  })
+
+  test("with native functions", async () => {
+    const { VM } = await import("#vm")
+    const bytecode = toBytecode(`
+      LOAD match
+      PUSH "hello world"
+      PUSH /world/
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const vm = new VM(bytecode)
+
+    // Register a native function that takes a string and regex
+    vm.set('match', (str: string, pattern: RegExp) => {
+      return pattern.test(str)
+    })
+
+    const result = await vm.run()
+    expect(result).toEqual({ type: 'boolean', value: true })
+  })
+
+  test("native function with regex replacement", async () => {
+    const { VM } = await import("#vm")
+    const bytecode = toBytecode(`
+      LOAD replace
+      PUSH "hello world"
+      PUSH /o/g
+      PUSH "0"
+      PUSH 3
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const vm = new VM(bytecode)
+
+    vm.set('replace', (str: string, pattern: RegExp, replacement: string) => {
+      return str.replace(pattern, replacement)
+    })
+
+    const result = await vm.run()
+    expect(result).toEqual({ type: 'string', value: 'hell0 w0rld' })
+  })
+
+  test("native function extracting matches", async () => {
+    const { VM } = await import("#vm")
+    const bytecode = toBytecode(`
+      LOAD extractNumbers
+      PUSH "test123abc456"
+      PUSH /\\d+/g
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const vm = new VM(bytecode)
+
+    vm.set('extractNumbers', (str: string, pattern: RegExp) => {
+      return str.match(pattern) || []
+    })
+
+    const result = await vm.run()
+    expect(result.type).toBe('array')
+    if (result.type === 'array') {
+      expect(result.value).toHaveLength(2)
+      expect(result.value[0]).toEqual({ type: 'string', value: '123' })
+      expect(result.value[1]).toEqual({ type: 'string', value: '456' })
+    }
+  })
+})

tests/repl.test.ts

@@ -0,0 +1,149 @@
+import { test, expect } from "bun:test"
+import { VM, toBytecode } from "#reef"
+
+test("REPL mode - demonstrates PC reset problem", async () => {
+  // Track how many times each line executes
+  let line1Count = 0
+  let line2Count = 0
+
+  // Line 1: Set x = 5, track execution
+  const line1 = toBytecode([
+    ["LOAD", "trackLine1"],
+    ["PUSH", 0],
+    ["PUSH", 0],
+    ["CALL"],
+    ["POP"],
+    ["PUSH", 5],
+    ["STORE", "x"]
+  ])
+
+  const vm = new VM(line1, {
+    trackLine1: () => { line1Count++; return null },
+    trackLine2: () => { line2Count++; return null }
+  })
+
+  await vm.run()
+  expect(vm.scope.get("x")).toEqual({ type: "number", value: 5 })
+  expect(line1Count).toBe(1)
+  expect(line2Count).toBe(0)
+
+  // Line 2: Track execution, load x
+  const line2 = toBytecode([
+    ["LOAD", "trackLine2"],
+    ["PUSH", 0],
+    ["PUSH", 0],
+    ["CALL"],
+    ["POP"],
+    ["LOAD", "x"]
+  ])
+
+  // Append line2 bytecode to VM (what a REPL would do)
+  vm.instructions.push(...line2.instructions)
+  for (const constant of line2.constants) {
+    if (!vm.constants.includes(constant)) {
+      vm.constants.push(constant)
+    }
+  }
+
+  // Current behavior: run() resets PC to 0, re-executing everything
+  await vm.run()
+
+  // PROBLEM: Line 1 ran AGAIN (count is now 2, not 1)
+  // This is the issue for REPL - side effects run multiple times
+  expect(line1Count).toBe(2) // Ran twice! Should still be 1
+  expect(line2Count).toBe(1) // This is correct
+
+  // What we WANT for REPL:
+  // - Only execute the NEW bytecode (line 2)
+  // - line1Count should stay at 1
+  // - line2Count should be 1
+})
+
+test("REPL mode - continue() executes only new bytecode", async () => {
+  // Track how many times each line executes
+  let line1Count = 0
+  let line2Count = 0
+
+  // Line 1: Set x = 5, track execution
+  const line1 = toBytecode([
+    ["LOAD", "trackLine1"],
+    ["PUSH", 0],
+    ["PUSH", 0],
+    ["CALL"],
+    ["POP"],
+    ["PUSH", 5],
+    ["STORE", "x"]
+  ])
+
+  const vm = new VM(line1, {
+    trackLine1: () => { line1Count++; return null },
+    trackLine2: () => { line2Count++; return null }
+  })
+
+  await vm.run()
+  expect(vm.scope.get("x")).toEqual({ type: "number", value: 5 })
+  expect(line1Count).toBe(1)
+  expect(line2Count).toBe(0)
+
+  // Line 2: Track execution, load x and add 10
+  const line2 = toBytecode([
+    ["LOAD", "trackLine2"],
+    ["PUSH", 0],
+    ["PUSH", 0],
+    ["CALL"],
+    ["POP"],
+    ["LOAD", "x"],
+    ["PUSH", 10],
+    ["ADD"]
+  ])
+
+  // Append line2 bytecode to VM using the helper method
+  vm.appendBytecode(line2)
+
+  // SOLUTION: Use continue() instead of run() to resume from current PC
+  await vm.continue()
+
+  const result = vm.stack[vm.stack.length - 1]
+
+  // SUCCESS: Line 1 only ran once, line 2 ran once
+  expect(line1Count).toBe(1) // Still 1! Side effect didn't re-run
+  expect(line2Count).toBe(1) // Ran once as expected
+  expect(result).toEqual({ type: "number", value: 15 }) // 5 + 10
+})
+
+test("REPL mode - function calls work across chunks", async () => {
+  const vm = new VM(toBytecode([]))
+  await vm.run()
+
+  // Line 1: Define a function
+  const line1 = toBytecode([
+    ["MAKE_FUNCTION", ["x"], ".body"],
+    ["STORE", "add1"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["PUSH", 1],
+    ["ADD"],
+    ["RETURN"],
+    [".end:"]
+  ])
+
+  vm.appendBytecode(line1)
+  await vm.continue()
+
+  expect(vm.scope.get("add1")?.type).toBe("function")
+
+  // Line 2: Call the function
+  const line2 = toBytecode([
+    ["LOAD", "add1"],
+    ["PUSH", 10],
+    ["PUSH", 1],
+    ["PUSH", 0],
+    ["CALL"]
+  ])
+
+  vm.appendBytecode(line2)
+  const result = await vm.continue()
+
+  expect(result).toEqual({ type: "number", value: 11 })
+})

tests/scope.test.ts

@@ -0,0 +1,243 @@
+import { test, expect } from "bun:test"
+import { Scope, toValue } from "#reef"
+
+test("Scope - create empty scope", () => {
+  const scope = new Scope()
+  expect(scope.parent).toBeUndefined()
+  expect(scope.locals.size).toBe(0)
+})
+
+test("Scope - create child scope with parent", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  expect(child.parent).toBe(parent)
+  expect(child.locals.size).toBe(0)
+})
+
+test("Scope - set and get variable in same scope", () => {
+  const scope = new Scope()
+  const value = toValue(42)
+
+  scope.set("x", value)
+  expect(scope.get("x")).toBe(value)
+})
+
+test("Scope - get returns undefined for non-existent variable", () => {
+  const scope = new Scope()
+  expect(scope.get("x")).toBeUndefined()
+})
+
+test("Scope - set updates existing variable in same scope", () => {
+  const scope = new Scope()
+
+  scope.set("x", toValue(10))
+  expect(scope.get("x")).toEqual({ type: "number", value: 10 })
+
+  scope.set("x", toValue(20))
+  expect(scope.get("x")).toEqual({ type: "number", value: 20 })
+})
+
+test("Scope - get searches parent scope", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(42))
+  expect(child.get("x")).toEqual({ type: "number", value: 42 })
+})
+
+test("Scope - get searches multiple levels up", () => {
+  const grandparent = new Scope()
+  const parent = new Scope(grandparent)
+  const child = new Scope(parent)
+
+  grandparent.set("x", toValue(100))
+  expect(child.get("x")).toEqual({ type: "number", value: 100 })
+})
+
+test("Scope - child updates parent variable when it exists (no shadowing)", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(10))
+  child.set("x", toValue(20))
+
+  // set() updates parent's variable, not shadow it
+  expect(parent.get("x")).toEqual({ type: "number", value: 20 })
+  expect(child.get("x")).toEqual({ type: "number", value: 20 })
+  expect(child.locals.has("x")).toBe(false)
+})
+
+test("Scope - set updates parent scope variable when it exists", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(10))
+  child.set("x", toValue(20))
+
+  // Should update parent's variable, not create new local one
+  expect(parent.get("x")).toEqual({ type: "number", value: 20 })
+  expect(child.get("x")).toEqual({ type: "number", value: 20 })
+  expect(child.locals.has("x")).toBe(false)
+})
+
+test("Scope - set creates new local variable when not found in parent", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(10))
+  child.set("y", toValue(20))
+
+  expect(parent.get("x")).toEqual({ type: "number", value: 10 })
+  expect(parent.get("y")).toBeUndefined()
+  expect(child.get("x")).toEqual({ type: "number", value: 10 })
+  expect(child.get("y")).toEqual({ type: "number", value: 20 })
+  expect(child.locals.has("y")).toBe(true)
+})
+
+test("Scope - has returns true for variable in current scope", () => {
+  const scope = new Scope()
+  scope.set("x", toValue(42))
+
+  expect(scope.has("x")).toBe(true)
+  expect(scope.has("y")).toBe(false)
+})
+
+test("Scope - has returns true for variable in parent scope", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(42))
+
+  expect(child.has("x")).toBe(true)
+  expect(child.has("y")).toBe(false)
+})
+
+test("Scope - has searches multiple levels up", () => {
+  const grandparent = new Scope()
+  const parent = new Scope(grandparent)
+  const child = new Scope(parent)
+
+  grandparent.set("x", toValue(100))
+
+  expect(child.has("x")).toBe(true)
+  expect(parent.has("x")).toBe(true)
+  expect(grandparent.has("x")).toBe(true)
+})
+
+test("Scope.vars() - returns empty array for empty scope", () => {
+  const scope = new Scope()
+  expect(scope.vars()).toEqual([])
+})
+
+test("Scope.vars() - returns single variable from current scope", () => {
+  const scope = new Scope()
+  scope.set("x", toValue(42))
+
+  expect(scope.vars()).toEqual(["x"])
+})
+
+test("Scope.vars() - returns multiple variables from current scope", () => {
+  const scope = new Scope()
+  scope.set("x", toValue(1))
+  scope.set("y", toValue(2))
+  scope.set("z", toValue(3))
+
+  const vars = scope.vars()
+  expect(vars.length).toBe(3)
+  expect(vars).toContain("x")
+  expect(vars).toContain("y")
+  expect(vars).toContain("z")
+})
+
+test("Scope.vars() - includes variables from parent scope", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(1))
+  child.set("y", toValue(2))
+
+  const vars = child.vars()
+  expect(vars.length).toBe(2)
+  expect(vars).toContain("x")
+  expect(vars).toContain("y")
+})
+
+test("Scope.vars() - includes variables from multiple parent scopes", () => {
+  const grandparent = new Scope()
+  const parent = new Scope(grandparent)
+  const child = new Scope(parent)
+
+  grandparent.set("x", toValue(1))
+  parent.set("y", toValue(2))
+  child.set("z", toValue(3))
+
+  const vars = child.vars()
+  expect(vars.length).toBe(3)
+  expect(vars).toContain("x")
+  expect(vars).toContain("y")
+  expect(vars).toContain("z")
+})
+
+test("Scope.vars() - no duplicates when child updates parent variable", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(10))
+  child.set("x", toValue(20))  // Updates parent, doesn't create local
+
+  // Only one "x" since child doesn't have its own local x
+  const vars = child.vars()
+  expect(vars).toEqual(["x"])
+})
+
+test("Scope.vars() - can't have duplicates if manually set in locals", () => {
+  const parent = new Scope()
+  const child = new Scope(parent)
+
+  parent.set("x", toValue(10))
+  child.locals.set("x", toValue(20))
+  const vars = child.vars()
+  expect(vars).toEqual(["x"])
+
+  expect(child.get("x")).toEqual({ type: "number", value: 20 })
+  expect(parent.get("x")).toEqual({ type: "number", value: 10 })
+})
+
+test("Scope.vars() - handles deep scope chains", () => {
+  let scope = new Scope()
+
+  // Create a deep chain: level0 -> level1 -> ... -> level5
+  for (let i = 0; i < 5; i++) {
+    scope.set(`var${i}`, toValue(i))
+    scope = new Scope(scope)
+  }
+
+  // Final scope should have all variables from the chain
+  const vars = scope.vars()
+  expect(vars.length).toBe(5)
+  expect(vars).toContain("var0")
+  expect(vars).toContain("var1")
+  expect(vars).toContain("var2")
+  expect(vars).toContain("var3")
+  expect(vars).toContain("var4")
+})
+
+test("Scope - can store and retrieve functions", () => {
+  const scope = new Scope()
+
+  const fnValue = {
+    type: 'function' as const,
+    value: '<function>' as const,
+    params: ['x'],
+    defaults: {},
+    body: 0,
+    variadic: false,
+    named: false,
+    parentScope: scope
+  }
+
+  scope.set("myFunc", fnValue)
+  expect(scope.get("myFunc")).toBe(fnValue)
+  expect(scope.get("myFunc")?.type).toBe("function")
+})

tests/setup.ts

@@ -0,0 +1,249 @@
+import { expect } from "bun:test"
+import { toValue, fromValue, type Value, toBytecode, run, type Bytecode } from "#reef"
+import { isEqual } from "../src/value"
+
+declare module "bun:test" {
+  interface Matchers<T> {
+    /**
+     * Run bytecode and assert that the result equals a JavaScript value after conversion via toValue()
+     * @example expect(bytecode).toEqualValue(42)
+     * @example expect("PUSH 5\nPUSH 3\nADD").toEqualValue(8)
+     * @example expect([["PUSH", 42]]).toEqualValue(42)
+     */
+    toEqualValue(expected: any): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is null
+     * @example expect(bytecode).toBeNull()
+     * @example expect("PUSH null").toBeNull()
+     */
+    toBeNull(): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is a boolean with the expected value
+     * @example expect(bytecode).toBeBoolean(true)
+     * @example expect("PUSH true").toBeBoolean(true)
+     */
+    toBeBoolean(expected: boolean): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is a number with the expected value
+     * @example expect(bytecode).toBeNumber(42)
+     * @example expect("PUSH 42").toBeNumber(42)
+     */
+    toBeNumber(expected: number): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is a string with the expected value
+     * @example expect(bytecode).toBeString("hello")
+     * @example expect("PUSH \"hello\"").toBeString("hello")
+     */
+    toBeString(expected: string): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is an array with the expected values
+     * @example expect(bytecode).toBeArray([1, 2, 3])
+     */
+    toBeArray(expected: any[]): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is a dict with the expected key-value pairs
+     * @example expect(bytecode).toBeDict({ x: 10, y: 20 })
+     */
+    toBeDict(expected: Record<string, any>): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is a function (Reef or native)
+     * @example expect(bytecode).toBeFunction()
+     */
+    toBeFunction(): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is truthy according to ReefVM semantics
+     * (only null and false are falsy)
+     * @example expect(bytecode).toBeTruthy()
+     */
+    toBeTruthy(): Promise<void>
+
+    /**
+     * Run bytecode and assert that the result is falsy according to ReefVM semantics
+     * (only null and false are falsy)
+     * @example expect(bytecode).toBeFalsy()
+     */
+    toBeFalsy(): Promise<void>
+  }
+}
+
+expect.extend({
+  async toEqualValue(this: void, received: unknown, expected: any) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const expectedValue = toValue(expected)
+    const pass = isEqual(result, expectedValue)
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to equal ${formatValue(expectedValue)}, but it did`
+          : `Expected value to equal ${formatValue(expectedValue)}, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeNull(this: void, received: unknown) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const pass = result.type === "null"
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be null, but it was`
+          : `Expected value to be null, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeBoolean(this: void, received: unknown, expected: boolean) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const pass = result.type === "boolean" && result.value === expected
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be boolean ${expected}, but it was`
+          : `Expected value to be boolean ${expected}, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeNumber(this: void, received: unknown, expected: number) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const pass = result.type === "number" && result.value === expected
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be number ${expected}, but it was`
+          : `Expected value to be number ${expected}, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeString(this: void, received: unknown, expected: string) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const pass = result.type === "string" && result.value === expected
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be string "${expected}", but it was`
+          : `Expected value to be string "${expected}", but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeArray(this: void, received: unknown, expected: any[]) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const expectedValue = toValue(expected)
+    const pass = result.type === "array" && isEqual(result, expectedValue)
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be array ${formatValue(expectedValue)}, but it was`
+          : `Expected value to be array ${formatValue(expectedValue)}, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeDict(this: void, received: unknown, expected: Record<string, any>) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const expectedValue = toValue(expected)
+    const pass = result.type === "dict" && isEqual(result, expectedValue)
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be dict ${formatValue(expectedValue)}, but it was`
+          : `Expected value to be dict ${formatValue(expectedValue)}, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeFunction(this: void, received: unknown) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    const pass = result.type === "function" || result.type === "native"
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be a function, but it was`
+          : `Expected value to be a function, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeTruthy(this: void, received: unknown) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    // ReefVM semantics: only null and false are falsy
+    const pass = !(result.type === "null" || (result.type === "boolean" && !result.value))
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be truthy, but it was: ${formatValue(result)}`
+          : `Expected value to be truthy, but received ${formatValue(result)}`,
+    }
+  },
+
+  async toBeFalsy(this: void, received: unknown) {
+    const bytecode = typeof received === "string" || Array.isArray(received) ? toBytecode(received as string | any[]) : received as Bytecode
+    const result = await run(bytecode)
+    // ReefVM semantics: only null and false are falsy
+    const pass = result.type === "null" || (result.type === "boolean" && !result.value)
+
+    return {
+      pass,
+      message: () =>
+        pass
+          ? `Expected value NOT to be falsy, but it was: ${formatValue(result)}`
+          : `Expected value to be falsy, but received ${formatValue(result)}`,
+    }
+  },
+})
+
+function formatValue(value: Value): string {
+  switch (value.type) {
+    case "null":
+      return "null"
+    case "boolean":
+    case "number":
+      return String(value.value)
+    case "string":
+      return `"${value.value}"`
+    case "array":
+      return `[${value.value.map(formatValue).join(", ")}]`
+    case "dict": {
+      const entries = Array.from(value.value.entries())
+        .map(([k, v]) => `${k}: ${formatValue(v)}`)
+        .join(", ")
+      return `{${entries}}`
+    }
+    case "regex":
+      return String(value.value)
+    case "function":
+    case "native":
+      return "<function>"
+    default:
+      return String(value)
+  }
+}

tests/unicode.test.ts

@@ -0,0 +1,119 @@
+import { test, expect, describe } from "bun:test"
+import { run } from "#index"
+import { toBytecode } from "#bytecode"
+
+describe("Unicode and Emoji", () => {
+  test("emoji variable names - string format", async () => {
+    const bytecode = toBytecode(`
+      PUSH 5
+      STORE 💎
+      LOAD 💎
+      HALT
+    `)
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 5 })
+  })
+
+  test("emoji variable names - array format", async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 100],
+      ["STORE", "💰"],
+      ["LOAD", "💰"],
+      ["PUSH", 50],
+      ["ADD"],
+      ["HALT"]
+    ])
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 150 })
+  })
+
+  test("unicode variable names - Japanese", async () => {
+    const bytecode = toBytecode(`
+      PUSH 42
+      STORE 変数
+      LOAD 変数
+      HALT
+    `)
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 42 })
+  })
+
+  test("unicode variable names - Chinese", async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 888],
+      ["STORE", "数字"],
+      ["LOAD", "数字"],
+      ["HALT"]
+    ])
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 888 })
+  })
+
+  test("emoji in function parameters", async () => {
+    const bytecode = toBytecode(`
+      MAKE_FUNCTION (💎 🌟) .add
+      STORE add
+      JUMP .after
+      .add:
+      LOAD 💎
+      LOAD 🌟
+      ADD
+      RETURN
+      .after:
+      LOAD add
+      PUSH 10
+      PUSH 20
+      PUSH 2
+      PUSH 0
+      CALL
+      HALT
+    `)
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 30 })
+  })
+
+  test("emoji with defaults and variadic", async () => {
+    const bytecode = toBytecode([
+      ["MAKE_FUNCTION", ["🎯=100", "...🎨"], ".fn"],
+      ["STORE", "fn"],
+      ["JUMP", ".after"],
+      [".fn:"],
+      ["LOAD", "🎯"],
+      ["RETURN"],
+      [".after:"],
+      ["LOAD", "fn"],
+      ["PUSH", 0],
+      ["PUSH", 0],
+      ["CALL"],
+      ["HALT"]
+    ])
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 100 })
+  })
+
+  test("mixed emoji and regular names", async () => {
+    const bytecode = toBytecode([
+      ["PUSH", 10],
+      ["STORE", "💎"],
+      ["PUSH", 20],
+      ["STORE", "value"],
+      ["PUSH", 30],
+      ["STORE", "🌟"],
+      ["LOAD", "💎"],
+      ["LOAD", "value"],
+      ["ADD"],
+      ["LOAD", "🌟"],
+      ["ADD"],
+      ["HALT"]
+    ])
+
+    const result = await run(bytecode)
+    expect(result).toEqual({ type: 'number', value: 60 })
+  })
+})

tests/validator.test.ts

@@ -201,17 +201,17 @@ test("formatValidationErrors produces readable output", () => {
   expect(formatted).toContain("UNKNOWN")
 })
 
-test("detects JUMP without # or .label", () => {
+test("detects JUMP without .label", () => {
   const source = `
     JUMP 5
     HALT
   `
   const result = validateBytecode(source)
   expect(result.valid).toBe(false)
-  expect(result.errors[0]!.message).toContain("JUMP requires immediate (#number) or label (.label)")
+  expect(result.errors[0]!.message).toContain("JUMP requires label (.label)")
 })
 
-test("detects JUMP_IF_TRUE without # or .label", () => {
+test("detects JUMP_IF_TRUE without .label", () => {
   const source = `
     PUSH true
     JUMP_IF_TRUE 2
@@ -219,10 +219,10 @@ test("detects JUMP_IF_TRUE without # or .label", () => {
   `
   const result = validateBytecode(source)
   expect(result.valid).toBe(false)
-  expect(result.errors[0]!.message).toContain("JUMP_IF_TRUE requires immediate (#number) or label (.label)")
+  expect(result.errors[0]!.message).toContain("JUMP_IF_TRUE requires label (.label)")
 })
 
-test("detects JUMP_IF_FALSE without # or .label", () => {
+test("detects JUMP_IF_FALSE without .label", () => {
   const source = `
     PUSH false
     JUMP_IF_FALSE 2
@@ -230,17 +230,18 @@ test("detects JUMP_IF_FALSE without # or .label", () => {
   `
   const result = validateBytecode(source)
   expect(result.valid).toBe(false)
-  expect(result.errors[0]!.message).toContain("JUMP_IF_FALSE requires immediate (#number) or label (.label)")
+  expect(result.errors[0]!.message).toContain("JUMP_IF_FALSE requires label (.label)")
 })
 
-test("allows JUMP with immediate number", () => {
+test("rejects JUMP with immediate number", () => {
   const source = `
     JUMP #2
     PUSH 999
     HALT
   `
   const result = validateBytecode(source)
-  expect(result.valid).toBe(true)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("JUMP requires label (.label)")
 })
 
 test("detects MAKE_ARRAY without #", () => {

tests/value.test.ts

@@ -0,0 +1,302 @@
+import { test, expect } from "bun:test"
+import { isValue, toValue } from "#reef"
+
+test("isValue - recognizes valid Value objects", () => {
+  expect(isValue({ type: 'number', value: 42 })).toBe(true)
+  expect(isValue({ type: 'number', value: 0 })).toBe(true)
+  expect(isValue({ type: 'string', value: 'hello' })).toBe(true)
+  expect(isValue({ type: 'string', value: '' })).toBe(true)
+  expect(isValue({ type: 'boolean', value: true })).toBe(true)
+  expect(isValue({ type: 'boolean', value: false })).toBe(true)
+  expect(isValue({ type: 'null', value: null })).toBe(true)
+  expect(isValue({ type: 'array', value: [] })).toBe(true)
+  expect(isValue({ type: 'array', value: [toValue(1), toValue(2)] })).toBe(true)
+  expect(isValue({ type: 'dict', value: new Map() })).toBe(true)
+  expect(isValue({ type: 'regex', value: /test/ })).toBe(true)
+  expect(isValue({
+    type: 'function',
+    value: '<function>',
+    params: [],
+    defaults: {},
+    body: 0,
+    variadic: false,
+    named: false,
+    parentScope: null as any
+  })).toBe(true)
+  expect(isValue({
+    type: 'native',
+    value: '<function>',
+    fn: (() => { }) as any
+  })).toBe(true)
+})
+
+test("isValue - rejects primitives", () => {
+  expect(isValue(42)).toBe(false)
+  expect(isValue(0)).toBe(false)
+  expect(isValue('hello')).toBe(false)
+  expect(isValue('')).toBe(false)
+  expect(isValue(true)).toBe(false)
+  expect(isValue(false)).toBe(false)
+  expect(isValue(null)).toBe(false)
+  expect(isValue(undefined)).toBe(false)
+})
+
+test("isValue - rejects plain objects", () => {
+  expect(isValue({})).toBe(false)
+  expect(isValue({ foo: 'bar' })).toBe(false)
+  expect(isValue({ type: 'number' })).toBe(false)
+  expect(isValue({ value: 42 })).toBe(false)
+})
+
+test("isValue - rejects arrays and functions", () => {
+  expect(isValue([])).toBe(false)
+  expect(isValue([1, 2, 3])).toBe(false)
+  expect(isValue(() => { })).toBe(false)
+  expect(isValue(function () { })).toBe(false)
+})
+
+test("isValue - rejects other object types", () => {
+  expect(isValue(new Date())).toBe(false)
+  expect(isValue(/regex/)).toBe(false)
+  expect(isValue(new Map())).toBe(false)
+  expect(isValue(new Set())).toBe(false)
+})
+
+test("isValue - used by toValue to detect already-converted values", () => {
+  const value = toValue(42)
+  expect(isValue(value)).toBe(true)
+
+  const result = toValue(value)
+  expect(result).toBe(value)
+})
+
+test("isValue - edge cases with type and value properties", () => {
+  expect(isValue({ type: 'number', value: 42, extra: 'data' })).toBe(true)
+
+  expect(isValue({ type: null, value: 42 })).toBe(false)
+  expect(isValue({ type: 'number', value: undefined })).toBe(true)
+
+  expect(isValue({ type: 'number', val: 42 })).toBe(false)
+  expect(isValue({ typ: 'number', value: 42 })).toBe(false)
+})
+
+test("isValue - rejects objects with invalid type values", () => {
+  expect(isValue({ type: 'text', value: 'Bob' })).toBe(false)
+  expect(isValue({ type: 'email', value: 'test@example.com' })).toBe(false)
+  expect(isValue({ type: 'password', value: 'secret' })).toBe(false)
+  expect(isValue({ type: 'checkbox', value: true })).toBe(false)
+  expect(isValue({ type: 'custom', value: 123 })).toBe(false)
+  expect(isValue({ type: 'unknown', value: null })).toBe(false)
+})
+
+test("toValue - correctly handles HTML input props", async () => {
+  const { VM, toBytecode, toValue } = await import("#reef")
+
+  const bytecode = toBytecode([["HALT"]])
+  const vm = new VM(bytecode)
+
+  const inputProps = { type: 'text', value: 'Bob' }
+  const converted = toValue(inputProps, vm)
+
+  expect(converted.type).toBe('dict')
+  expect(converted.value.get('type')).toEqual({ type: 'string', value: 'text' })
+  expect(converted.value.get('value')).toEqual({ type: 'string', value: 'Bob' })
+})
+
+test("toValue - converts wrapped Reef functions back to original Value", async () => {
+  const { VM, toBytecode, fnFromValue } = await import("#reef")
+
+  // Create a Reef function
+  const bytecode = toBytecode([
+    ["MAKE_FUNCTION", ["x"], ".body"],
+    ["STORE", "add1"],
+    ["JUMP", ".end"],
+    [".body:"],
+    ["LOAD", "x"],
+    ["PUSH", 1],
+    ["ADD"],
+    ["RETURN"],
+    [".end:"],
+    ["HALT"]
+  ])
+
+  const vm = new VM(bytecode)
+  await vm.run()
+
+  const reefFunction = vm.scope.get("add1")!
+  expect(reefFunction.type).toBe("function")
+
+  // Convert to JS function
+  const jsFunction = fnFromValue(reefFunction, vm)
+  expect(typeof jsFunction).toBe("function")
+
+  // Convert back to Value - should return the original Reef function
+  const backToValue = toValue(jsFunction)
+  expect(backToValue).toBe(reefFunction)  // Same reference
+  expect(backToValue.type).toBe("function")
+})
+
+test("fromValue - converts native function back to original JS function", async () => {
+  const { VM, toBytecode, toValue, fromValue } = await import("#reef")
+
+  const bytecode = toBytecode([["HALT"]])
+  const vm = new VM(bytecode)
+
+  // Create a native JS function
+  const originalFn = (x: number, y: number) => x * y
+
+  // Convert to Value (wraps it as a native function)
+  const nativeValue = toValue(originalFn, vm)
+  expect(nativeValue.type).toBe("native")
+
+  // Convert back to JS - should get the original function
+  const convertedFn = fromValue(nativeValue, vm)
+  expect(typeof convertedFn).toBe("function")
+
+  // Verify it's the same function
+  expect(convertedFn).toBe(originalFn)
+
+  // Verify it works correctly
+  expect(convertedFn(3, 4)).toBe(12)
+})
+
+test("fromValue - native function roundtrip preserves functionality", async () => {
+  const { VM, toBytecode, toValue, fromValue } = await import("#reef")
+
+  const bytecode = toBytecode([["HALT"]])
+  const vm = new VM(bytecode)
+
+  // Create a native function with state
+  let callCount = 0
+  const countingFn = (n: number) => {
+    callCount++
+    return n * callCount
+  }
+
+  // Roundtrip through Value
+  const nativeValue = toValue(countingFn, vm)
+  const roundtrippedFn = fromValue(nativeValue, vm)
+
+  // Verify it maintains state across calls
+  expect(roundtrippedFn(10)).toBe(10)  // 10 * 1
+  expect(roundtrippedFn(10)).toBe(20)  // 10 * 2
+  expect(roundtrippedFn(10)).toBe(30)  // 10 * 3
+  expect(callCount).toBe(3)
+})
+
+test("fromValue - async native function roundtrip", async () => {
+  const { VM, toBytecode, toValue, fromValue } = await import("#reef")
+
+  const bytecode = toBytecode([["HALT"]])
+  const vm = new VM(bytecode)
+
+  const asyncFn = async (x: number, y: number) => {
+    await new Promise(resolve => setTimeout(resolve, 1))
+    return x + y
+  }
+
+  const nativeValue = toValue(asyncFn, vm)
+  expect(nativeValue.type).toBe("native")
+
+  const roundtrippedFn = fromValue(nativeValue, vm)
+
+  const result = await roundtrippedFn(5, 7)
+  expect(result).toBe(12)
+})
+
+test("toValue - throws helpful error when calling function converted without VM", async () => {
+  function myFunction(x: number) {
+    return x * 2
+  }
+
+  const value = toValue(myFunction)
+  expect(value.type).toBe('native')
+
+  // Error is thrown when calling the function, not when converting
+  await expect(async () => {
+    await value.fn({ type: 'number', value: 5 })
+  }).toThrow(/can't call function that was converted without a vm/)
+
+  await expect(async () => {
+    await value.fn({ type: 'number', value: 5 })
+  }).toThrow(/Function: myFunction/)
+
+  await expect(async () => {
+    await value.fn({ type: 'number', value: 5 })
+  }).toThrow(/Source:/)
+
+  await expect(async () => {
+    await value.fn({ type: 'number', value: 5 })
+  }).toThrow(/Called from:/)
+})
+
+test("toValue - error message shows function info for arrow functions", async () => {
+  const anonymousFn = (x: number) => x * 2
+
+  const value = toValue(anonymousFn)
+  expect(value.type).toBe('native')
+
+  // Arrow functions show as <anonymous>
+  await expect(async () => {
+    await value.fn({ type: 'number', value: 5 })
+  }).toThrow(/Function: <anonymous>/)
+
+  await expect(async () => {
+    await value.fn({ type: 'number', value: 5 })
+  }).toThrow(/Source:/)
+})
+
+test("toValue - error when function is nested in object without VM", async () => {
+  const obj = {
+    name: "test",
+    handler: (x: number) => x * 2
+  }
+
+  const value = toValue(obj)
+  expect(value.type).toBe('dict')
+
+  const handlerValue = value.value.get('handler')!
+  expect(handlerValue.type).toBe('native')
+
+  await expect(async () => {
+    await (handlerValue as any).fn({ type: 'number', value: 5 })
+  }).toThrow(/can't call function that was converted without a vm/)
+
+  await expect(async () => {
+    await (handlerValue as any).fn({ type: 'number', value: 5 })
+  }).toThrow(/Function: handler/)
+})
+
+test("toValue - error when function is nested in array without VM", async () => {
+  const arr = [1, 2, (x: number) => x * 2]
+
+  const value = toValue(arr)
+  expect(value.type).toBe('array')
+
+  const fnValue = value.value[2]!
+  expect(fnValue.type).toBe('native')
+
+  await expect(async () => {
+    await (fnValue as any).fn({ type: 'number', value: 5 })
+  }).toThrow(/can't call function that was converted without a vm/)
+})
+
+test("fromValue - throws helpful error when converting function without VM", async () => {
+  const { Scope, fromValue } = await import("#reef")
+
+  const reefFunction = {
+    type: 'function' as const,
+    params: ['x', 'y'],
+    defaults: {},
+    body: 10,
+    parentScope: new Scope(),
+    variadic: false,
+    named: false,
+    value: '<function>' as const
+  }
+
+  expect(() => fromValue(reefFunction)).toThrow(/VM is required for function conversion/)
+  expect(() => fromValue(reefFunction)).toThrow(/Function params: \[x, y\]/)
+  expect(() => fromValue(reefFunction)).toThrow(/Function body at instruction: 10/)
+  expect(() => fromValue(reefFunction)).toThrow(/Called from:/)
+})

tests/vm.test.ts

@@ -0,0 +1,54 @@
+import { test, expect, describe } from "bun:test"
+import { VM } from "#vm"
+import { toBytecode } from "#bytecode"
+import { toValue } from "#value"
+
+describe("VM scope methods", () => {
+  test("pushScope creates isolated child scope", async () => {
+    const bytecode = toBytecode([["HALT"]])
+    const vm = new VM(bytecode)
+
+    vm.set("x", 42)
+    vm.pushScope()
+
+    const xValue = vm.scope.get("x")
+    expect(xValue).toEqual({ type: "number", value: 42 })
+
+    vm.set("y", 100)
+    expect(vm.scope.get("x")).toEqual({ type: "number", value: 42 })
+    expect(vm.scope.get("y")).toEqual({ type: "number", value: 100 })
+  })
+
+  test("popScope returns to parent scope and child variables are not accessible", async () => {
+    const bytecode = toBytecode([["HALT"]])
+    const vm = new VM(bytecode)
+
+    vm.set("x", 42)
+    vm.pushScope()
+    vm.set("y", 100)
+
+    expect(vm.scope.get("x")).toEqual({ type: "number", value: 42 })
+    expect(vm.scope.get("y")).toEqual({ type: "number", value: 100 })
+
+    vm.popScope()
+    expect(vm.scope.get("x")).toEqual({ type: "number", value: 42 })
+    expect(vm.scope.get("y")).toBeUndefined()
+  })
+
+  test("pushScope with locals initializes child scope with variables", async () => {
+    const bytecode = toBytecode([["HALT"]])
+    const vm = new VM(bytecode)
+
+    vm.set("x", 42)
+    vm.pushScope({ y: 100, z: "hello" })
+
+    expect(vm.scope.get("x")).toEqual({ type: "number", value: 42 })
+    expect(vm.scope.get("y")).toEqual({ type: "number", value: 100 })
+    expect(vm.scope.get("z")).toEqual({ type: "string", value: "hello" })
+
+    vm.popScope()
+    expect(vm.scope.get("x")).toEqual({ type: "number", value: 42 })
+    expect(vm.scope.get("y")).toBeUndefined()
+    expect(vm.scope.get("z")).toBeUndefined()
+  })
+})