add var? and var

src/prelude/index.ts

@@ -1,7 +1,7 @@
 // The prelude creates all the builtin Shrimp functions.
 
 import {
-  type Value, toValue,
+  type Value, type VM, toValue,
   extractParamInfo, isWrapped, getOriginalFunction,
 } from 'reefvm'
 
@@ -34,13 +34,11 @@ export const globals = {
     const val = toValue(v)
     return `#<${val.type}: ${formatValue(val)}>`
   },
-  length: (v: any) => {
+  var: function (this: VM, v: any) {
-    const value = toValue(v)
+    return typeof v === 'string' ? this.scope.get(v) : v
-    switch (value.type) {
+  },
-      case 'string': case 'array': return value.value.length
+  'var?': function (this: VM, v: string) {
-      case 'dict': return value.value.size
+    return typeof v !== 'string' || this.scope.has(v)
-      default: throw new Error(`length: expected string, array, or dict, got ${value.type}`)
-    }
   },
 
   // type predicates
@@ -65,6 +63,14 @@ export const globals = {
   identity: (v: any) => v,
 
   // collections
+  length: (v: any) => {
+    const value = toValue(v)
+    switch (value.type) {
+      case 'string': case 'array': return value.value.length
+      case 'dict': return value.value.size
+      default: throw new Error(`length: expected string, array, or dict, got ${value.type}`)
+    }
+  },
   at: (collection: any, index: number | string) => {
     const value = toValue(collection)
     if (value.type === 'string' || value.type === 'array') {

src/prelude/tests/info.test.ts

@@ -1,5 +1,25 @@
 import { expect, describe, test } from 'bun:test'
-import { globals, colors } from '#prelude'
+import { globals } from '#prelude'
+
+describe('var and var?', () => {
+  test('var? checks if a variable exists', async () => {
+    await expect(`var? 'nada'`).toEvaluateTo(false, globals)
+    await expect(`var? 'info'`).toEvaluateTo(false, globals)
+    await expect(`abc = abc; var? 'abc'`).toEvaluateTo(true, globals)
+    await expect(`var? 'var?'`).toEvaluateTo(true, globals)
+
+    await expect(`var? 'dict'`).toEvaluateTo(true, globals)
+    await expect(`var? dict`).toEvaluateTo(true, globals)
+  })
+
+  test('var returns a value or null', async () => {
+    await expect(`var 'nada'`).toEvaluateTo(null, globals)
+    await expect(`var nada`).toEvaluateTo(null, globals)
+    await expect(`var 'info'`).toEvaluateTo(null, globals)
+    await expect(`abc = my-string; var 'abc'`).toEvaluateTo('my-string', globals)
+    await expect(`abc = my-string; var abc`).toEvaluateTo(null, globals)
+  })
+})
 
 describe('type predicates', () => {
   test('string? checks for string type', async () => {
@@ -38,7 +58,6 @@ describe('type predicates', () => {
   })
 })
 
-
 describe('introspection', () => {
   test('type returns proper types', async () => {
     await expect(`type 'hello'`).toEvaluateTo('string', globals)
@@ -50,18 +69,6 @@ describe('introspection', () => {
     await expect(`type [a=1 b=2]`).toEvaluateTo('dict', globals)
   })
 
-  test('length', async () => {
-    await expect(`length 'hello'`).toEvaluateTo(5, globals)
-    await expect(`length [1 2 3]`).toEvaluateTo(3, globals)
-    await expect(`length [a=1 b=2]`).toEvaluateTo(2, globals)
-  })
-
-  test('length throws on invalid types', async () => {
-    await expect(`try: length 42 catch e: 'error' end`).toEvaluateTo('error', globals)
-    await expect(`try: length true catch e: 'error' end`).toEvaluateTo('error', globals)
-    await expect(`try: length null catch e: 'error' end`).toEvaluateTo('error', globals)
-  })
-
   test('inspect formats values', async () => {
     await expect(`inspect 'hello'`).toEvaluateTo("\u001b[32m'hello\u001b[32m'\u001b[0m", globals)
   })

src/prelude/tests/prelude.test.ts

@@ -125,6 +125,18 @@ describe('utilities', () => {
 })
 
 describe('collections', () => {
+  test('length', async () => {
+    await expect(`length 'hello'`).toEvaluateTo(5, globals)
+    await expect(`length [1 2 3]`).toEvaluateTo(3, globals)
+    await expect(`length [a=1 b=2]`).toEvaluateTo(2, globals)
+  })
+
+  test('length throws on invalid types', async () => {
+    await expect(`try: length 42 catch e: 'error' end`).toEvaluateTo('error', globals)
+    await expect(`try: length true catch e: 'error' end`).toEvaluateTo('error', globals)
+    await expect(`try: length null catch e: 'error' end`).toEvaluateTo('error', globals)
+  })
+
   test('literal array creates array from arguments', async () => {
     await expect(`[ 1 2 3 ]`).toEvaluateTo([1, 2, 3], globals)
     await expect(`['a' 'b']`).toEvaluateTo(['a', 'b'], globals)