diff --git a/bin/repl b/bin/repl
index 052f481..c6ff98c 100755
--- a/bin/repl
+++ b/bin/repl
@@ -144,19 +144,33 @@ async function repl() {
       return
     }
 
-    codeHistory.push(trimmed)
-
     try {
       const compiler = new Compiler(trimmed, Object.keys(globals))
 
-      vm.appendBytecode(compiler.bytecode)
+      // Save VM state before appending bytecode, in case execution fails
+      const savedInstructions = [...vm.instructions]
+      const savedConstants = [...vm.constants]
+      const savedPc = vm.pc
+      const savedScope = vm.scope
+      const savedStopped = vm.stopped
 
-      const result = await vm.continue()
+      try {
+        vm.appendBytecode(compiler.bytecode)
+        const result = await vm.continue()
 
-      console.log(`${colors.dim}=>${colors.reset} ${formatValue(result)}`)
+        codeHistory.push(trimmed)
+        console.log(`${colors.dim}=>${colors.reset} ${formatValue(result)}`)
+      } catch (error: any) {
+        vm.instructions = savedInstructions
+        vm.constants = savedConstants
+        vm.pc = savedPc
+        vm.scope = savedScope
+        vm.stopped = savedStopped
+
+        console.log(`\n${colors.red}Error:${colors.reset} ${error.message}`)
+      }
     } catch (error: any) {
       console.log(`\n${colors.red}Error:${colors.reset} ${error.message}`)
-      codeHistory.pop()
     }
 
     rl.prompt()
diff --git a/bun.lock b/bun.lock
index 005ca60..afb8aaa 100644
--- a/bun.lock
+++ b/bun.lock
@@ -62,7 +62,7 @@
 
     "hono": ["hono@4.9.8", "", {}, "sha512-JW8Bb4RFWD9iOKxg5PbUarBYGM99IcxFl2FPBo2gSJO11jjUDqlP1Bmfyqt8Z/dGhIQ63PMA9LdcLefXyIasyg=="],
 
-    "reefvm": ["reefvm@git+https://git.nose.space/defunkt/reefvm#030eb7487165b3ba502965a8b7fa09c4b5fdb0da", { "peerDependencies": { "typescript": "^5" } }, "030eb7487165b3ba502965a8b7fa09c4b5fdb0da"],
+    "reefvm": ["reefvm@git+https://git.nose.space/defunkt/reefvm#c69b172c78853756ec8acba5bc33d93eb6a571c6", { "peerDependencies": { "typescript": "^5" } }, "c69b172c78853756ec8acba5bc33d93eb6a571c6"],
 
     "style-mod": ["style-mod@4.1.2", "", {}, "sha512-wnD1HyVqpJUI2+eKZ+eo1UwghftP6yuFheBqqe+bWCotBjC2K1YnteJILRMs3SM4V/0dLEW1SC27MWP5y+mwmw=="],
 
diff --git a/package.json b/package.json
index 2ac8e0c..cdf55cc 100644
--- a/package.json
+++ b/package.json
@@ -7,7 +7,7 @@
     "dev": "bun generate-parser && bun --hot src/server/server.tsx",
     "generate-parser": "lezer-generator src/parser/shrimp.grammar --typeScript -o src/parser/shrimp.ts",
     "repl": "bun generate-parser && bun bin/repl",
-    "update-reef": "cd packages/ReefVM && git pull origin main"
+    "update-reef": "rm -rf ~/.bun/install/cache/ && bun update reefvm"
   },
   "dependencies": {
     "@codemirror/view": "^6.38.3",
diff --git a/src/prelude/list.ts b/src/prelude/list.ts
index eb013ef..ec38e23 100644
--- a/src/prelude/list.ts
+++ b/src/prelude/list.ts
@@ -1,3 +1,5 @@
+import { type Value, toValue, toNull } from 'reefvm'
+
 export const list = {
   slice: (list: any[], start: number, end?: number) => list.slice(start, end),
   map: async (list: any[], cb: Function) => {
@@ -40,9 +42,41 @@ export const list = {
     return true
   },
 
+  // mutating
+  push: (list: Value, item: Value) => {
+    if (list.type !== 'array') return toNull()
+    return toValue(list.value.push(item))
+  },
+  pop: (list: Value) => {
+    if (list.type !== 'array') return toNull()
+    return toValue(list.value.pop())
+  },
+  shift: (list: Value) => {
+    if (list.type !== 'array') return toNull()
+    return toValue(list.value.shift())
+  },
+  unshift: (list: Value, item: Value) => {
+    if (list.type !== 'array') return toNull()
+    return toValue(list.value.unshift(item))
+  },
+  splice: (list: Value, start: Value, deleteCount: Value, ...items: Value[]) => {
+    const realList = list.value as any[]
+    const realStart = start.value as number
+    const realDeleteCount = deleteCount.value as number
+    const realItems = items.map(item => item.value)
+    return toValue(realList.splice(realStart, realDeleteCount, ...realItems))
+  },
+
   // sequence operations
   reverse: (list: any[]) => list.slice().reverse(),
-  sort: (list: any[], cb?: (a: any, b: any) => number) => list.slice().sort(cb),
+  sort: async (list: any[], cb?: (a: any, b: any) => number) => {
+    const arr = [...list]
+    if (!cb) return arr.sort()
+    for (let i = 0; i < arr.length; i++)
+      for (let j = i + 1; j < arr.length; j++)
+        if ((await cb(arr[i], arr[j])) > 0) [arr[i], arr[j]] = [arr[j], arr[i]]
+    return arr
+  },
   concat: (...lists: any[][]) => lists.flat(1),
   flatten: (list: any[], depth: number = 1) => list.flat(depth),
   unique: (list: any[]) => Array.from(new Set(list)),
@@ -86,4 +120,13 @@ export const list = {
     }
     return groups
   },
-}
\ No newline at end of file
+}
+
+
+  // raw functions deal directly in Value types, meaning we can modify collection
+  // careful - they MUST return a Value!
+  ; (list.splice as any).raw = true
+  ; (list.push as any).raw = true
+  ; (list.pop as any).raw = true
+  ; (list.shift as any).raw = true
+  ; (list.unshift as any).raw = true
\ No newline at end of file
diff --git a/src/prelude/tests/prelude.test.ts b/src/prelude/tests/prelude.test.ts
index ef7d8d6..f061e29 100644
--- a/src/prelude/tests/prelude.test.ts
+++ b/src/prelude/tests/prelude.test.ts
@@ -341,6 +341,84 @@ describe('collections', () => {
     await expect(`list.index-of [1 2 3] 5`).toEvaluateTo(-1, globals)
   })
 
+  test('list.push adds to end and mutates array', async () => {
+    await expect(`arr = [1 2]; list.push arr 3; arr`).toEvaluateTo([1, 2, 3], globals)
+  })
+
+  test('list.push returns the size of the array', async () => {
+    await expect(`arr = [1 2]; arr | list.push 3`).toEvaluateTo(3, globals)
+  })
+
+  test('list.pop removes from end and mutates array', async () => {
+    await expect(`arr = [1 2 3]; list.pop arr; arr`).toEvaluateTo([1, 2], globals)
+  })
+
+  test('list.pop returns removed element', async () => {
+    await expect(`list.pop [1 2 3]`).toEvaluateTo(3, globals)
+  })
+
+  test('list.pop returns null for empty array', async () => {
+    await expect(`list.pop []`).toEvaluateTo(null, globals)
+  })
+
+  test('list.shift removes from start and mutates array', async () => {
+    await expect(`arr = [1 2 3]; list.shift arr; arr`).toEvaluateTo([2, 3], globals)
+  })
+
+  test('list.shift returns removed element', async () => {
+    await expect(`list.shift [1 2 3]`).toEvaluateTo(1, globals)
+  })
+
+  test('list.shift returns null for empty array', async () => {
+    await expect(`list.shift []`).toEvaluateTo(null, globals)
+  })
+
+  test('list.unshift adds to start and mutates array', async () => {
+    await expect(`arr = [2 3]; list.unshift arr 1; arr`).toEvaluateTo([1, 2, 3], globals)
+  })
+
+  test('list.unshift returns the length of the array', async () => {
+    await expect(`arr = [2 3]; arr | list.unshift 1`).toEvaluateTo(3, globals)
+  })
+
+  test('list.splice removes elements and mutates array', async () => {
+    await expect(`arr = [1 2 3 4 5]; list.splice arr 1 2; arr`).toEvaluateTo([1, 4, 5], globals)
+  })
+
+  test('list.splice returns removed elements', async () => {
+    await expect(`list.splice [1 2 3 4 5] 1 2`).toEvaluateTo([2, 3], globals)
+  })
+
+  test('list.splice from start', async () => {
+    await expect(`list.splice [1 2 3 4 5] 0 2`).toEvaluateTo([1, 2], globals)
+  })
+
+  test('list.splice to end', async () => {
+    await expect(`arr = [1 2 3 4 5]; list.splice arr 3 2; arr`).toEvaluateTo([1, 2, 3], globals)
+  })
+
+  test('list.sort with no callback sorts ascending', async () => {
+    await expect(`list.sort [3 1 4 1 5] null`).toEvaluateTo([1, 1, 3, 4, 5], globals)
+  })
+
+  test('list.sort with callback sorts using comparator', async () => {
+    await expect(`
+      desc = do a b:
+        b - a
+      end
+      list.sort [3 1 4 1 5] desc
+    `).toEvaluateTo([5, 4, 3, 1, 1], globals)
+  })
+
+  test('list.sort with callback for strings by length', async () => {
+    await expect(`
+      by-length = do a b:
+        (length a) - (length b)
+      end
+      list.sort ['cat' 'a' 'dog' 'elephant'] by-length
+    `).toEvaluateTo(['a', 'cat', 'dog', 'elephant'], globals)
+  })
+
   test('list.any? checks if any element matches', async () => {
     await expect(`
       gt-three = do x: x > 3 end