feat(codemode): support generator functions (#38172)

packages/codemode/interpreter-support.md

@@ -29,7 +29,8 @@ ultimate source of truth.
 ## Values and literals
 
 - [x] `null`, `undefined`, booleans, finite and non-finite numbers, and strings.
-- [x] Array literals, including holes and spread from arrays, strings, Maps, Sets, and URLSearchParams.
+- [x] Array literals, including holes and spread from arrays, strings, Maps, Sets, URLSearchParams, custom synchronous
+      iterators, and synchronous generators.
 - [x] Object literals with shorthand, computed string/number keys, and spread from plain data objects; `null` and
       `undefined` are no-ops, while arrays are rejected.
 - [x] Template literals with interpolation.
@@ -57,7 +58,9 @@ ultimate source of truth.
 - [ ] Hoist function declarations accepted directly in switch cases.
 - [x] Computed object destructuring keys such as `const { [field]: value } = record`.
 - [x] Object destructuring from arrays, such as `const { length } = values`.
-- [x] Array destructuring from supported non-array iterables: strings, Maps, Sets, and URLSearchParams.
+- [x] Array binding and assignment destructuring from strings, Maps, Sets, URLSearchParams, custom synchronous
+      iterators, and synchronous generators, including stepwise elisions/rest and `IteratorClose` on early completion
+      or binding/default failure.
 
 ## Statements and control flow
 
@@ -65,7 +68,8 @@ ultimate source of truth.
 - [x] `if`/`else` and conditional expressions.
 - [x] `switch`, including default clauses and fallthrough.
 - [x] `for`, `while`, and `do...while`.
-- [x] `for...of` over arrays, strings, Maps, Sets, and URLSearchParams.
+- [x] `for...of` over arrays, strings, Maps, Sets, URLSearchParams, custom synchronous iterators, and confined
+      synchronous generators. Abrupt completion invokes the iterator's optional `return()`.
 - [x] `for...in` over own keys of plain objects, arrays, and tool references.
 - [x] Unlabeled `break` and `continue`.
 - [x] `try`, `catch`, optional catch bindings, and `finally`.
@@ -75,7 +79,7 @@ ultimate source of truth.
       `Symbol.asyncIterator` or the `Symbol.iterator` fallback. Each iterator step is sequential, yielded promises and
       plain values from synchronous collections and sync iterators are awaited before binding, and abrupt loop
       completion invokes the iterator's optional `return()`. Custom async iterators control their yielded values, as in
-      JavaScript; only their `next()` results are awaited. Async generators remain outside the supported subset.
+      JavaScript; only their `next()` results are awaited. Confined sync and async generators are iterable here.
 
 ## Functions and callbacks
 
@@ -104,7 +108,27 @@ ultimate source of truth.
 - [ ] User-defined constructor calls.
 - [ ] `Function.prototype.call`, `apply`, and `bind` for CodeMode functions.
 - [ ] Classes and private fields.
-- [ ] Generator functions and `yield`.
+- [x] Synchronous and async generator declarations/expressions, `yield`, and `yield*`, including lazy bodies,
+      `next(value)`, `return(value)`, `throw(value)`, exhaustion, promise adoption, async request ordering,
+      `try`/`catch`/`finally`, and sync/async iterator symbols. Async `yield*` awaits values while adapting a sync
+      iterator but preserves values supplied by a manually implemented async iterator. Generator values are opaque
+      runtime references.
+- [x] Synchronous generators and custom synchronous iterators are consumed stepwise by array/argument spread, array
+      destructuring, `Array.from`, Map/Set/URLSearchParams construction, `Object.fromEntries`, Object/Map `groupBy`,
+      Promise combinators, `AggregateError`, and `Math.sumPrecise`. Mapper/grouping callbacks interleave with iterator
+      steps; synchronous consumers preserve yielded promise objects rather than awaiting them. Async generators are
+      rejected by every synchronous consumer.
+- [x] Synchronous iterator acquisition and result validation follow `IteratorClose` boundaries: consumer errors and
+      intentional early stops invoke `return()`, acquisition/`next()` failures do not, and an original consumer error
+      wins over a cleanup failure. Async iterator consumption remains limited to `for await...of` and async `yield*`.
+- [x] Portable generator protocol coverage is adapted from pinned Test262 cases for suspended-start, suspended-yield,
+      and completed states; sync and async `next`/`return`/`throw`; finally yields and completion overrides; rejected
+      yielded promises; mixed async request queues; sync and async `yield*` forwarding; malformed methods/results;
+      and declaration, expression, and object-method forms with closure and parameter behavior. The adapted suite
+      deliberately skips Test262 variants whose observation mechanism requires unsupported getter definitions,
+      proxies, prototype inspection or mutation, non-arrow `this`, classes, or arbitrary symbols. It also skips tests
+      asserting exact promise reaction-turn counts beyond the observable ordering guarantee documented below. These
+      are interpreter-surface boundaries, not claims that the corresponding full Test262 families pass unchanged.
 
 ## Expressions and operators
 
@@ -130,8 +154,8 @@ ultimate source of truth.
 - [x] Tool calls start eagerly and return supervised, run-once CodeMode promises.
 - [x] Direct `await`, repeated awaits, and implicit resolution when a promise is returned from a function/program.
 - [x] `Promise.resolve` and `Promise.reject`.
-- [x] `Promise.all`, `Promise.allSettled`, `Promise.race`, and `Promise.any` over supported collections containing
-      promises and plain values.
+- [x] `Promise.all`, `Promise.allSettled`, `Promise.race`, and `Promise.any` over finite collections, custom synchronous
+      iterators, and synchronous generators containing promises and plain values.
 - [x] `Promise.all` preserves result order and rejects on the first observed failure without cancelling siblings.
 - [x] `Promise.allSettled` returns plain fulfilled/rejected outcome records.
 - [x] `Promise.race` settles from the first result without cancelling losers at settlement time.
@@ -175,14 +199,16 @@ ultimate source of truth.
 - [x] `Object()` and `new Object()` return `{}` for nullish arguments and pass objects through unchanged;
       primitive wrapper objects (`Object(1)`) are rejected explicitly.
 - [x] Computed property names and object spread.
-- [x] `Object.keys`, `Object.values`, `Object.entries`, `Object.hasOwn`, `Object.assign`, and `Object.fromEntries`.
+- [x] `Object.keys`, `Object.values`, `Object.entries`, `Object.hasOwn`, `Object.assign`, and `Object.fromEntries`, with
+      synchronous iterator support for `fromEntries`.
 - [x] `Object.keys` over arrays and tool references.
 - [x] Object identity is preserved by in-CodeMode Object helpers.
 - [x] Prototype traversal and mutation through `__proto__`, `constructor`, and `prototype` are blocked.
 - [ ] Legal own data fields named `__proto__`, `constructor`, or `prototype` are rejected at JSON/tool boundaries and
       cannot be created, read, or written in CodeMode; tool path segments with those names remain supported.
 - [x] `Object.is` for supported data values.
-- [x] `Object.groupBy` over supported collection iterables, with string-key coercion and null-prototype results.
+- [x] `Object.groupBy` over finite collections and custom synchronous iterators/generators, with string-key coercion
+      and null-prototype results.
 
 ## Arrays
 
@@ -190,7 +216,7 @@ ultimate source of truth.
       array of that length; invalid lengths throw `RangeError`. Iteration, spread, join, and JSON handle holes like
       JavaScript, and host results normalize holes to `null`.
 - [x] Static methods: `Array.isArray`, `Array.of`, and `Array.from`, including the `Array.from` mapper form with
-      `(value, index)` arguments.
+      `(value, index)` arguments and stepwise synchronous iterator consumption.
 - [x] Iteration/transformation: `map`, `filter`, `flatMap`, and `forEach`.
 - [x] Searching/tests: `find`, `findIndex`, `findLast`, `findLastIndex`, `some`, `every`, `includes`, `indexOf`, and
       `lastIndexOf`.
@@ -245,7 +271,8 @@ ultimate source of truth.
       for feature detection. Calling any undefined value reports a native-style `TypeError` naming the callee, for
       example `Math.sum is not a function.` Blocked members (`constructor`, `__proto__`, ...) still throw,
       and unknown `Promise` statics keep their descriptive error.
-- [x] `Math.sumPrecise` over supported collection iterables, rejecting non-number elements without coercion.
+- [x] `Math.sumPrecise` over finite collections and custom synchronous iterators/generators, rejecting non-number
+      elements without coercion.
 - [x] Global coercing `isFinite` and `isNaN`; opaque runtime references reject as data errors, like `Number(...)`.
 
 ## JSON and console
@@ -297,10 +324,10 @@ ultimate source of truth.
 
 ## Map and Set
 
-- [x] Static `Map.groupBy` over supported collection iterables, preserving key identity.
-- [x] `new Map()` from entry arrays or another Map.
+- [x] Static `Map.groupBy` over finite collections and custom synchronous iterators/generators, preserving key identity.
+- [x] `new Map()` from synchronous iterables of entries.
 - [x] Map `get`, `set`, `has`, `delete`, `clear`, `size`, and `forEach`.
-- [x] `new Set()` from arrays, strings, or another Set.
+- [x] `new Set()` from synchronous iterables.
 - [x] Set `add`, `has`, `delete`, `clear`, `size`, and `forEach`.
 - [x] Materialized `keys`, `values`, and `entries` arrays for Map and Set.
 - [x] Spread, `for...of`, `Array.from`, and `Object.fromEntries` integration.
@@ -316,7 +343,7 @@ ultimate source of truth.
 - [x] Readable URL fields: `href`, `origin`, `protocol`, `username`, `password`, `host`, `hostname`, `port`,
       `pathname`, `search`, and `hash`.
 - [x] Writable URL fields except `origin`.
-- [x] `new URLSearchParams()` from query strings, data objects, pairs, Maps, and URLSearchParams.
+- [x] `new URLSearchParams()` from query strings, data objects, synchronous iterables of pairs, and URLSearchParams.
 - [x] URLSearchParams `append`, `delete`, `get`, `getAll`, `has`, `set`, `sort`, `forEach`, `keys`, `values`,
       `entries`, `toString`, and `size`.
 - [x] URL values serialize to their href; URLSearchParams serialize to `{}`.
@@ -326,7 +353,7 @@ ultimate source of truth.
 - [x] `Error`, `TypeError`, `RangeError`, `SyntaxError`, `ReferenceError`, `EvalError`, and `URIError`, callable with
       or without `new`.
 - [x] `AggregateError` with the `(errors, message?)` signature and an own `errors` array, constructed directly or by
-      an all-rejected `Promise.any`.
+      an all-rejected `Promise.any`; direct construction accepts custom synchronous iterators and generators.
 - [x] Error `name`/`message`, error inheritance through `instanceof`, and plain-data serialization.
 - [x] `instanceof` for Date, RegExp, Map, Set, URL, URLSearchParams, Array, Object, Promise, and Error types.
 - [x] Catchable user throws, runtime failures raised during interpreted evaluation, awaited tool failures, and awaited

packages/codemode/src/interpreter/errors.ts

@@ -1,9 +1,10 @@
+import { Effect } from "effect"
 import type { Diagnostic } from "../codemode.js"
 import { ToolError } from "../tool-error.js"
 import { copyOut, ToolRuntimeError, type SafeObject } from "../tool-runtime.js"
 import { type AstNode, formatLocation, InterpreterRuntimeError, ProgramThrow, sourceLocation } from "./model.js"
 import { containsRuntimeReference } from "./references.js"
-import { spreadItems } from "../stdlib/collections.js"
+import { type SyncIteratorRunner } from "./iterator.js"
 import { coerceToString, createAggregateErrorValue, createErrorValue, errorConstructors } from "../stdlib/value.js"
 
 export const normalizeError = (error: unknown): Diagnostic => {
@@ -79,15 +80,27 @@ export const caughtErrorValue = (thrown: unknown): unknown => {
   return createErrorValue(name, normalizeError(thrown).message)
 }
 
-export const constructErrorValue = (name: string, args: Array<unknown>, node: AstNode): SafeObject => {
-  if (name !== "AggregateError") return createErrorValue(name, args[0] === undefined ? "" : coerceToString(args[0]))
-  const errors = spreadItems(args[0])
-  if (errors === undefined) {
-    throw new InterpreterRuntimeError(
-      "new AggregateError(...) expects an array of errors (e.g. new AggregateError(errors, message?)).",
-      node,
-    ).as("TypeError")
-  }
-  // Error values must not alias caller-owned arrays.
-  return createAggregateErrorValue([...errors], args[1] === undefined ? "" : coerceToString(args[1]))
-}
+export const constructErrorValue = (name: string, args: Array<unknown>): SafeObject =>
+  createErrorValue(name, args[0] === undefined ? "" : coerceToString(args[0]))
+
+export const constructAggregateErrorValue = <R>(
+  runner: SyncIteratorRunner<R>,
+  args: Array<unknown>,
+  node: AstNode,
+): Effect.Effect<SafeObject, unknown, R> =>
+  Effect.gen(function* () {
+    const cursor = yield* runner.syncIterator(args[0], node)
+    if (cursor === undefined) {
+      throw new InterpreterRuntimeError("new AggregateError(...) expects a synchronous iterable of errors.", node).as(
+        "TypeError",
+      )
+    }
+    const errors: Array<unknown> = []
+    while (true) {
+      const step = yield* cursor.next
+      if (step.done) {
+        return createAggregateErrorValue(errors, args[1] === undefined ? "" : coerceToString(args[1]))
+      }
+      errors.push(step.value)
+    }
+  })

packages/codemode/src/interpreter/iterator.ts

@@ -0,0 +1,21 @@
+import { Effect, Exit } from "effect"
+import type { AstNode } from "./model.js"
+
+export type IteratorCursor<R> = {
+  readonly next: Effect.Effect<{ readonly done: boolean; readonly value: unknown }, unknown, R>
+  readonly close: Effect.Effect<void, unknown, R>
+}
+
+export type SyncIteratorRunner<R> = {
+  readonly syncIterator: (value: unknown, node: AstNode) => Effect.Effect<IteratorCursor<R> | undefined, unknown, R>
+}
+
+export const preserveConsumerError = <A, R>(
+  cursor: IteratorCursor<R>,
+  effect: Effect.Effect<A, unknown, R>,
+): Effect.Effect<A, unknown, R> =>
+  Effect.flatMap(Effect.exit(effect), (exit) =>
+    Exit.isSuccess(exit)
+      ? Effect.succeed(exit.value)
+      : Effect.andThen(Effect.exit(cursor.close), Effect.failCause(exit.cause)),
+  )

packages/codemode/src/interpreter/methods.ts

@@ -2,6 +2,7 @@ import { Effect } from "effect"
 import {
   type AstNode,
   CodeModeFunction,
+  CodeModeGenerator,
   CoercionFunction,
   ErrorConstructorReference,
   GlobalMethodReference,
@@ -33,6 +34,7 @@ import { invokeRegExpMethod, invokeRegExpStatic, matchToValue, toHostRegex } fro
 import { invokeStringStatic } from "../stdlib/string.js"
 import { invokeURLMethod, invokeURLStatic, uriArgument } from "../stdlib/url.js"
 import { boundedData, coerceToNumber, coerceToString, errorBrandName } from "../stdlib/value.js"
+import { preserveConsumerError, type SyncIteratorRunner } from "./iterator.js"
 
 export type CallbackRunner<R> = {
   readonly invokeFunction: (fn: CodeModeFunction, args: Array<unknown>) => Effect.Effect<unknown, unknown, R>
@@ -360,19 +362,12 @@ const invokeArrayStatic = (name: string, args: Array<unknown>, node: AstNode): u
       return Array.isArray(args[0])
     case "of":
       return [...args]
-    case "from":
-      return arrayFromItems(args[0], node)
     default:
       throw new InterpreterRuntimeError(`Array.${name} is not available.`, node)
   }
 }
 
-const arrayFromItems = (source: unknown, node: AstNode): Array<unknown> => {
-  if (source instanceof CodeModeMap) return Array.from(source.map.entries(), ([key, item]) => [key, item])
-  if (source instanceof CodeModeSet) return Array.from(source.set.values())
-  if (source instanceof CodeModeURLSearchParams) {
-    return Array.from(source.params.entries(), ([key, value]) => [key, value])
-  }
+const arrayLikeSource = (source: unknown, node: AstNode): { readonly length: number; readonly source: object } => {
   if (source instanceof CodeModePromise) {
     throw new InterpreterRuntimeError(
       "Array.from received an un-awaited Promise; await it before creating the array.",
@@ -380,15 +375,16 @@ const arrayFromItems = (source: unknown, node: AstNode): Array<unknown> => {
       "InvalidDataValue",
     )
   }
-  if (typeof source === "string") return Array.from(source)
-  if (Array.isArray(source)) return [...source]
   if (
     source !== null &&
     typeof source === "object" &&
     (Object.getPrototypeOf(source) === Object.prototype || Object.getPrototypeOf(source) === null) &&
     typeof (source as { length?: unknown }).length === "number"
   ) {
-    return Array.from(source as ArrayLike<unknown>)
+    const length = (source as { length: number }).length
+    const normalized = Number.isNaN(length) || length <= 0 ? 0 : Math.trunc(length)
+    if (normalized > 4_294_967_295) throw new RangeError("Invalid array length")
+    return { length: normalized, source }
   }
   throw new InterpreterRuntimeError(
     "Array.from expects an array, string, Map, Set, or array-like value.",
@@ -398,24 +394,42 @@ const arrayFromItems = (source: unknown, node: AstNode): Array<unknown> => {
 }
 
 export const invokeArrayFrom = <R>(
-  runner: CallbackRunner<R>,
+  runner: CallbackRunner<R> & SyncIteratorRunner<R>,
   args: Array<unknown>,
   node: AstNode,
 ): Effect.Effect<unknown, unknown, R> => {
-  const items = arrayFromItems(args[0], node)
-  if (args.length < 2 || args[1] === undefined) return Effect.succeed(items)
-  const apply = applyCollectionCallback(runner, args[1], "Array.from", node)
+  const source = args[0]
+  const apply =
+    args.length < 2 || args[1] === undefined ? undefined : applyCollectionCallback(runner, args[1], "Array.from", node)
   return Effect.gen(function* () {
-    const values: Array<unknown> = []
-    for (let index = 0; index < items.length; index += 1) {
-      values.push(yield* apply([items[index], index]))
+    const cursor = yield* runner.syncIterator(source, node)
+    if (cursor === undefined) {
+      if (source instanceof CodeModeGenerator) {
+        throw new InterpreterRuntimeError("Array.from expects a synchronous iterable or array-like value.", node).as(
+          "TypeError",
+        )
+      }
+      const arrayLike = arrayLikeSource(source, node)
+      const values: Array<unknown> = []
+      for (let index = 0; index < arrayLike.length; index += 1) {
+        const item = Reflect.get(arrayLike.source, index)
+        values.push(apply === undefined ? item : yield* apply([item, index]))
+      }
+      return values
+    }
+    const values: Array<unknown> = []
+    let index = 0
+    while (true) {
+      const step = yield* cursor.next
+      if (step.done) return values
+      values.push(apply === undefined ? step.value : yield* preserveConsumerError(cursor, apply([step.value, index])))
+      index += 1
     }
-    return values
   })
 }
 
 export const invokeGroupBy = <R>(
-  runner: CallbackRunner<R>,
+  runner: CallbackRunner<R> & SyncIteratorRunner<R>,
   namespace: "Map" | "Object",
   args: Array<unknown>,
   node: AstNode,
@@ -425,47 +439,50 @@ export const invokeGroupBy = <R>(
     throw new InterpreterRuntimeError(`${namespace}.groupBy expects an iterable collection.`, node).as("TypeError")
   }
   const apply = applyCollectionCallback(runner, args[1], `${namespace}.groupBy`, node)
-  const items = supportedIterableItems(source)
-  if (items === undefined) {
-    throw new InterpreterRuntimeError(`${namespace}.groupBy expects an iterable collection.`, node).as("TypeError")
-  }
   return Effect.gen(function* () {
+    const cursor = yield* runner.syncIterator(source, node)
+    if (cursor === undefined) {
+      throw new InterpreterRuntimeError(`${namespace}.groupBy expects an iterable collection.`, node).as("TypeError")
+    }
     if (namespace === "Map") {
       const result = new CodeModeMap()
       let index = 0
-      for (const item of items) {
-        const key = yield* apply([item, index])
+      while (true) {
+        const step = yield* cursor.next
+        if (step.done) return result
+        const item = step.value
+        const key = yield* preserveConsumerError(cursor, apply([item, index]))
         const group = result.map.get(key)
         if (group === undefined) result.map.set(key, [item])
         else (group as Array<unknown>).push(item)
         index += 1
       }
-      return result
     }
 
     const result: SafeObject = Object.create(null) as SafeObject
     let index = 0
-    for (const item of items) {
-      const key = yield* coerceGroupByPropertyKey(runner, yield* apply([item, index]), node)
+    while (true) {
+      const step = yield* cursor.next
+      if (step.done) return result
+      const item = step.value
+      const key = yield* preserveConsumerError(
+        cursor,
+        Effect.flatMap(apply([item, index]), (value) => coerceGroupByPropertyKey(runner, value, node)),
+      )
       if (isBlockedMember(key)) {
-        throw new InterpreterRuntimeError(`Property '${key}' is not available.`, node)
+        return yield* preserveConsumerError(
+          cursor,
+          Effect.fail(new InterpreterRuntimeError(`Property '${key}' is not available.`, node)),
+        )
       }
       const group = result[key]
       if (group === undefined) result[key] = [item]
       else (group as Array<unknown>).push(item)
       index += 1
     }
-    return result
   })
 }
 
-const supportedIterableItems = (source: unknown): Iterable<unknown> | undefined => {
-  if (Array.isArray(source) || typeof source === "string") return source
-  if (source instanceof CodeModeMap) return source.map.entries()
-  if (source instanceof CodeModeSet) return source.set.values()
-  if (source instanceof CodeModeURLSearchParams) return source.params.entries()
-}
-
 const coerceGroupByPropertyKey = <R>(
   runner: CallbackRunner<R>,
   value: unknown,

packages/codemode/src/interpreter/model.ts

@@ -1,3 +1,4 @@
+import type { Effect } from "effect"
 import type { SafeObject } from "../tool-runtime.js"
 import type { CodeModePromise, CodeModeRegExp, CodeModeURL } from "../values.js"
 
@@ -45,6 +46,27 @@ export class CodeModeFunction {
     readonly body: AstNode,
     readonly capturedScopes: ReadonlyArray<Map<string, Binding>>,
     readonly async: boolean,
+    readonly generator: boolean,
+  ) {}
+}
+
+export type GeneratorRequestKind = "next" | "return" | "throw"
+
+export class CodeModeGenerator {
+  constructor(
+    readonly asynchronous: boolean,
+    readonly request: (
+      kind: GeneratorRequestKind,
+      value: unknown,
+      node: AstNode,
+    ) => Effect.Effect<unknown, unknown, unknown>,
+  ) {}
+}
+
+export class GeneratorMethodReference {
+  constructor(
+    readonly generator: CodeModeGenerator,
+    readonly kind: GeneratorRequestKind | "iterator",
   ) {}
 }
 
@@ -128,6 +150,10 @@ export class ProgramThrow {
   constructor(readonly value: unknown) {}
 }
 
+export class GeneratorReturn {
+  constructor(readonly value: unknown) {}
+}
+
 export class ErrorConstructorReference {
   constructor(readonly name: string) {}
 }

packages/codemode/src/interpreter/promises.ts

@@ -13,9 +13,9 @@ import {
 import { caughtErrorValue, normalizeError } from "./errors.js"
 import { applyCollectionCallback, isSupportedCallback, type CallbackRunner, type SupportedCallback } from "./methods.js"
 import { typeofValue } from "./references.js"
-import { spreadItems } from "../stdlib/collections.js"
 import { createAggregateErrorValue } from "../stdlib/value.js"
 import { CodeModePromise } from "../values.js"
+import type { SyncIteratorRunner } from "./iterator.js"
 
 // Observation only controls rejection reporting; program completion interrupts all promise work.
 export class PromiseRuntime<R> {
@@ -64,6 +64,10 @@ export class PromiseRuntime<R> {
     return Fiber.await(promise.fiber)
   }
 
+  fork(effect: Effect.Effect<unknown, unknown, R>): Effect.Effect<void, never, R> {
+    return Effect.asVoid(Effect.forkIn(effect, this.scope, { startImmediately: true }))
+  }
+
   diagnostics(): Array<Diagnostic> {
     return [...this.failures].sort(([left], [right]) => left - right).map(([, failure]) => failure)
   }
@@ -84,7 +88,7 @@ export const selfResolutionError = (node?: AstNode): InterpreterRuntimeError =>
   new InterpreterRuntimeError("Chaining cycle detected: a promise cannot resolve with itself.", node).as("TypeError")
 
 export const invokePromiseMethod = <R>(
-  runner: CallbackRunner<R>,
+  runner: CallbackRunner<R> & SyncIteratorRunner<R>,
   promises: PromiseRuntime<R>,
   ref: PromiseMethodReference,
   args: Array<unknown>,
@@ -98,79 +102,69 @@ export const invokePromiseMethod = <R>(
     return promises.create(Effect.fail(new ProgramThrow(args[0])))
   }
 
-  const spread = spreadItems(args[0])
-  if (spread === undefined) {
-    return promises.create(
-      Effect.fail(
-        new InterpreterRuntimeError(
-          `Promise.${ref.name} expects an array of promises or plain values (e.g. Promise.${ref.name}(items.map((item) => tools.ns.tool(item)))).`,
+  return promises.create(
+    Effect.gen(function* () {
+      const cursor = yield* runner.syncIterator(args[0], node)
+      if (cursor === undefined) {
+        throw new InterpreterRuntimeError(
+          `Promise.${ref.name} expects an array or other synchronous iterable.`,
           node,
-        ).as("TypeError"),
-      ),
-    )
-  }
-  const items = Array.from(spread)
+        ).as("TypeError")
+      }
+      const items: Array<unknown> = []
+      while (true) {
+        const step = yield* cursor.next
+        if (step.done) break
+        items.push(step.value)
+        if (step.value instanceof CodeModePromise) promises.markObserved(step.value)
+      }
 
-  for (const item of items) {
-    if (item instanceof CodeModePromise) promises.markObserved(item)
-  }
-
-  switch (ref.name) {
-    case "all": {
-      const observations = items.map((item) =>
-        item instanceof CodeModePromise ? Effect.flatten(promises.await(item)) : Effect.succeed(item),
-      )
-      return promises.create(settleAfterTurn(Effect.all(observations, { concurrency: "unbounded" })))
-    }
-    case "allSettled": {
-      const observations = items.map((item) =>
-        item instanceof CodeModePromise ? promises.await(item) : Effect.succeed(Exit.succeed(item)),
-      )
-      return promises.create(
-        settleAfterTurn(
-          Effect.gen(function* () {
-            const outcomes: Array<unknown> = []
-            for (const observation of observations) {
-              const exit = yield* observation
-              if (Exit.isSuccess(exit)) {
-                outcomes.push(
-                  Object.assign(Object.create(null) as SafeObject, { status: "fulfilled", value: exit.value }),
-                )
-                continue
-              }
-              if (Cause.hasInterruptsOnly(exit.cause)) {
-                // Teardown interruption is not a program-level rejection.
-                return yield* Effect.failCause(exit.cause)
-              }
-              outcomes.push(
-                Object.assign(Object.create(null) as SafeObject, {
-                  status: "rejected",
-                  reason: caughtErrorValue(Cause.squash(exit.cause)),
-                }),
-              )
-            }
-            return outcomes
-          }),
-        ),
-      )
-    }
-    case "race": {
-      if (items.length === 0) {
-        return promises.create(
-          Effect.fail(
-            new InterpreterRuntimeError(
-              "Promise.race([]) would never settle; provide at least one promise or value.",
-              node,
+      if (ref.name === "all") {
+        return yield* settleAfterTurn(
+          Effect.all(
+            items.map((item) =>
+              item instanceof CodeModePromise ? Effect.flatten(promises.await(item)) : Effect.succeed(item),
+            ),
+            { concurrency: "unbounded" },
+          ),
+        )
+      }
+      if (ref.name === "allSettled") {
+        const outcomes: Array<unknown> = []
+        for (const item of items) {
+          const exit = item instanceof CodeModePromise ? yield* promises.await(item) : Exit.succeed(item)
+          if (Exit.isSuccess(exit)) {
+            outcomes.push(Object.assign(Object.create(null) as SafeObject, { status: "fulfilled", value: exit.value }))
+            continue
+          }
+          if (Cause.hasInterruptsOnly(exit.cause)) return yield* Effect.failCause(exit.cause)
+          outcomes.push(
+            Object.assign(Object.create(null) as SafeObject, {
+              status: "rejected",
+              reason: caughtErrorValue(Cause.squash(exit.cause)),
+            }),
+          )
+        }
+        yield* Effect.yieldNow
+        return outcomes
+      }
+      if (ref.name === "race") {
+        if (items.length === 0) {
+          throw new InterpreterRuntimeError(
+            "Promise.race([]) would never settle; provide at least one promise or value.",
+            node,
+          )
+        }
+        return yield* settleAfterTurn(
+          Effect.flatten(
+            Effect.raceAll(
+              items.map((item) =>
+                item instanceof CodeModePromise ? promises.await(item) : Effect.succeed(Exit.succeed(item)),
+              ),
             ),
           ),
         )
       }
-      const observations = items.map((item) =>
-        item instanceof CodeModePromise ? promises.await(item) : Effect.succeed(Exit.succeed(item)),
-      )
-      return promises.create(settleAfterTurn(Effect.flatten(Effect.raceAll(observations))))
-    }
-    case "any": {
       const flipped = items.map((item) =>
         item instanceof CodeModePromise
           ? Effect.flatMap(promises.await(item), (exit) => {
@@ -180,17 +174,18 @@ export const invokePromiseMethod = <R>(
             })
           : Effect.fail(new PromiseAnyFulfilled(item)),
       )
-      const body = Effect.all(flipped, { concurrency: "unbounded" }).pipe(
-        Effect.flatMap((reasons) =>
-          Effect.fail(new ProgramThrow(createAggregateErrorValue(reasons, "All promises were rejected"))),
-        ),
-        Effect.catch((error) =>
-          error instanceof PromiseAnyFulfilled ? Effect.succeed(error.value) : Effect.fail(error),
+      return yield* settleAfterTurn(
+        Effect.all(flipped, { concurrency: "unbounded" }).pipe(
+          Effect.flatMap((reasons) =>
+            Effect.fail(new ProgramThrow(createAggregateErrorValue(reasons, "All promises were rejected"))),
+          ),
+          Effect.catch((error) =>
+            error instanceof PromiseAnyFulfilled ? Effect.succeed(error.value) : Effect.fail(error),
+          ),
         ),
       )
-      return promises.create(settleAfterTurn(body))
-    }
-  }
+    }),
+  )
 }
 
 export const invokePromiseInstanceMethod = <R>(

packages/codemode/src/interpreter/references.ts

@@ -1,10 +1,12 @@
 import {
   type AstNode,
   CodeModeFunction,
+  CodeModeGenerator,
   CoercionFunction,
   ErrorConstructorReference,
   GlobalMethodReference,
   GlobalNamespace,
+  GeneratorMethodReference,
   InterpreterRuntimeError,
   IntrinsicReference,
   JsonMethodReference,
@@ -21,6 +23,8 @@ import { isCodeModeValue, CodeModePromise } from "../values.js"
 
 export const isRuntimeReference = (value: unknown): boolean =>
   value instanceof CodeModeFunction ||
+  value instanceof CodeModeGenerator ||
+  value instanceof GeneratorMethodReference ||
   value instanceof ToolReference ||
   value instanceof IntrinsicReference ||
   value instanceof GlobalNamespace ||
@@ -107,6 +111,7 @@ export const rejectCircularInsertion = (container: object, value: unknown, label
 export const typeofValue = (value: unknown): string => {
   if (
     value instanceof CodeModeFunction ||
+    value instanceof GeneratorMethodReference ||
     value instanceof CoercionFunction ||
     value instanceof IntrinsicReference ||
     value instanceof GlobalMethodReference ||

packages/codemode/src/stdlib/math.ts

@@ -1,5 +1,6 @@
+import { Effect } from "effect"
+import { preserveConsumerError, type SyncIteratorRunner } from "../interpreter/iterator.js"
 import { type AstNode, InterpreterRuntimeError } from "../interpreter/model.js"
-import { spreadItems } from "./collections.js"
 
 // Bun exposes ES2026 Math.sumPrecise before TypeScript's standard library types.
 declare global {
@@ -53,17 +54,6 @@ export const mathMethods = new Set([
 export const invokeMathMethod = (name: string, args: Array<unknown>, node: AstNode): number => {
   if (!mathMethods.has(name)) throw new InterpreterRuntimeError(`Math.${name} is not available.`, node)
   if (name === "random") return Math.random()
-  if (name === "sumPrecise") {
-    const items = spreadItems(args[0])
-    if (items === undefined) {
-      throw new InterpreterRuntimeError("Math.sumPrecise expects an iterable collection.", node).as("TypeError")
-    }
-    const numbers = Array.from(items)
-    if (!numbers.every((item): item is number => typeof item === "number")) {
-      throw new InterpreterRuntimeError("Math.sumPrecise expects an iterable of numbers.", node).as("TypeError")
-    }
-    return Math.sumPrecise(numbers)
-  }
   // Validate only the arguments the method consumes; like JS, extras are ignored
   // (so built-ins work as callbacks receiving (element, index, array)).
   const num = (index: number): number => {
@@ -153,3 +143,29 @@ export const invokeMathMethod = (name: string, args: Array<unknown>, node: AstNo
   }
   throw new InterpreterRuntimeError(`Math.${name} is not available.`, node)
 }
+
+export const invokeMathSumPrecise = <R>(
+  runner: SyncIteratorRunner<R>,
+  source: unknown,
+  node: AstNode,
+): Effect.Effect<number, unknown, R> =>
+  Effect.gen(function* () {
+    const cursor = yield* runner.syncIterator(source, node)
+    if (cursor === undefined) {
+      throw new InterpreterRuntimeError("Math.sumPrecise expects a synchronous iterable.", node).as("TypeError")
+    }
+    const numbers: Array<number> = []
+    while (true) {
+      const step = yield* cursor.next
+      if (step.done) return Math.sumPrecise(numbers)
+      yield* preserveConsumerError(
+        cursor,
+        Effect.sync(() => {
+          if (typeof step.value !== "number") {
+            throw new InterpreterRuntimeError("Math.sumPrecise expects an iterable of numbers.", node).as("TypeError")
+          }
+          numbers.push(step.value)
+        }),
+      )
+    }
+  })

packages/codemode/src/stdlib/object.ts

@@ -1,3 +1,4 @@
+import { Effect } from "effect"
 import {
   type AstNode,
   AsyncIteratorSymbol,
@@ -7,8 +8,9 @@ import {
 } from "../interpreter/model.js"
 import { containsOpaqueReference } from "../interpreter/references.js"
 import { isBlockedMember } from "../tool-runtime.js"
-import { isCodeModeValue, CodeModeMap, CodeModePromise, CodeModeSet, CodeModeURLSearchParams } from "../values.js"
+import { isCodeModeValue, CodeModePromise } from "../values.js"
 import { boundedData, coerceToString } from "./value.js"
+import { preserveConsumerError, type SyncIteratorRunner } from "../interpreter/iterator.js"
 
 export const objectMethodsPreservingIdentity = new Set(["assign", "values", "entries", "fromEntries"])
 
@@ -39,11 +41,6 @@ export const invokeObjectMethod = (name: string, args: Array<unknown>, node: Ast
     if (isBlockedMember(key)) throw new InterpreterRuntimeError(`Property '${key}' is not available.`, node)
     out[key] = item
   }
-  const addEntry = (out: Record<string, unknown>, key: unknown, item: unknown): void => {
-    boundedData(key, "Object.fromEntries key")
-    boundedData(item, "Object.fromEntries value")
-    guardedSet(out, coerceToString(key), item)
-  }
   switch (name) {
     case "keys":
       return Object.keys(requireObject())
@@ -79,32 +76,47 @@ export const invokeObjectMethod = (name: string, args: Array<unknown>, node: Ast
       }
       return out
     }
-    case "fromEntries": {
-      if (args[0] instanceof CodeModeMap) {
-        const out: Record<string, unknown> = Object.create(null)
-        for (const [key, item] of args[0].map.entries()) addEntry(out, key, item)
-        return out
-      }
-      if (args[0] instanceof CodeModeURLSearchParams) {
-        const out: Record<string, unknown> = Object.create(null)
-        for (const [key, value] of args[0].params.entries()) guardedSet(out, key, value)
-        return out
-      }
-      const pairs = args[0] instanceof CodeModeSet ? Array.from(args[0].set.values()) : args[0]
-      if (!Array.isArray(pairs)) {
-        boundedData(args[0], "Object.fromEntries input")
-        throw new InterpreterRuntimeError("Object.fromEntries expects an array of [key, value] pairs.", node)
-      }
-      const out: Record<string, unknown> = Object.create(null)
-      for (const pair of pairs) {
-        const validated = boundedData(pair, "Object.fromEntries entry")
-        if (validated === null || typeof validated !== "object" || isCodeModeValue(validated))
-          throw new InterpreterRuntimeError("Object.fromEntries expects [key, value] entry objects.", node)
-        const entry = pair as Record<string, unknown>
-        addEntry(out, entry[0], entry[1])
-      }
-      return out
-    }
   }
   throw new InterpreterRuntimeError(`Object.${name} is not available.`, node)
 }
+
+export const invokeObjectFromEntries = <R>(
+  runner: SyncIteratorRunner<R>,
+  source: unknown,
+  node: AstNode,
+): Effect.Effect<Record<string, unknown>, unknown, R> => {
+  const out: Record<string, unknown> = Object.create(null)
+  return Effect.gen(function* () {
+    const cursor = yield* runner.syncIterator(source, node)
+    if (cursor === undefined) {
+      throw new InterpreterRuntimeError("Object.fromEntries expects a synchronous iterable of entries.", node).as(
+        "TypeError",
+      )
+    }
+    while (true) {
+      const step = yield* cursor.next
+      if (step.done) return out
+      yield* preserveConsumerError(
+        cursor,
+        Effect.sync(() => {
+          if (
+            step.value === null ||
+            typeof step.value !== "object" ||
+            isCodeModeValue(step.value) ||
+            containsOpaqueReference(step.value)
+          ) {
+            throw new InterpreterRuntimeError("Object.fromEntries expects [key, value] entry objects.", node).as(
+              "TypeError",
+            )
+          }
+          const entry = step.value as Record<string, unknown>
+          boundedData(entry[0], "Object.fromEntries key")
+          boundedData(entry[1], "Object.fromEntries value")
+          const key = coerceToString(entry[0])
+          if (isBlockedMember(key)) throw new InterpreterRuntimeError(`Property '${key}' is not available.`, node)
+          out[key] = entry[1]
+        }),
+      )
+    }
+  })
+}

packages/codemode/src/tool-runtime.ts

@@ -553,7 +553,7 @@ export const prepare = <R>(tools: Tools<R>, catalogBudget = defaultCatalogBudget
     "## Language",
     "",
     "Use common JavaScript data operations, functions, control flow, selected standard-library methods, and awaited tool calls. Built-ins include Date, RegExp, Map, Set, URL, URLSearchParams, and URI encoding helpers.",
-    "Modules/imports, classes, generators, timers, fetch, eval, prototype access, and unlisted methods are unavailable. Use tools for external operations. Use await with try/catch.",
+    "Modules/imports, classes, timers, fetch, eval, prototype access, and unlisted methods are unavailable. Use tools for external operations. Use await with try/catch.",
     "Prefer explicit `return`; otherwise only the final top-level expression becomes the result.",
     "Dates and URLs serialize to strings at data boundaries; Map/Set/RegExp/URLSearchParams serialize to `{}`.",
   ]

packages/codemode/test/codemode.test.ts

@@ -732,9 +732,10 @@ describe("CodeMode public contract", () => {
     expect(instructions).toContain("not a general-purpose runtime")
     expect(instructions).not.toContain("Standard modern JavaScript works")
     expect(instructions).not.toContain("TypeScript type annotations")
-    for (const missing of ["Modules/imports", "classes", "generators", "fetch"]) {
+    for (const missing of ["Modules/imports", "classes", "fetch"]) {
       expect(instructions).toContain(missing)
     }
+    expect(instructions).not.toContain("generators")
     expect(instructions).not.toContain("new Promise(...) are unavailable")
     expect(instructions).not.toContain("promise chaining")
     expect(instructions).toContain("URL, URLSearchParams, and URI encoding helpers")