ask262/engine262/src/intrinsics/Iterator.mts

import { AbruptCompletion, Q, type ValueEvaluator } from '../completion.mts';
import type { Mutable } from '../helpers.mts';
import { surroundingAgent } from '../host-defined/engine.mts';
import {
  ObjectValue,
  type BooleanValue,
  UndefinedValue,
  Value,
  type Arguments,
  type FunctionCallContext,
  wellKnownSymbols,
} from '../value.mts';
import { bootstrapConstructor } from './bootstrap.mts';
import {
  Call,
  CreateIteratorFromClosure,
  GetIteratorDirect,
  GetIteratorFlattenable,
  GetMethod,
  IteratorClose,
  IteratorStepValue,
  OrdinaryCreateFromConstructor,
  OrdinaryHasInstance,
  OrdinaryObjectCreate,
  Yield,
  type BuiltinFunctionObject,
  type FunctionObject,
  type IteratorObject,
  type Realm,
  type YieldEvaluator,
} from '#self';


/** https://tc39.es/ecma262/multipage/control-abstraction-objects.html#sec-iterator-constructor */
function* IteratorConstructor(
  this: BuiltinFunctionObject,
  _args: Arguments,
  { NewTarget }: FunctionCallContext,
): ValueEvaluator<ObjectValue> {
  // 1. If NewTarget is either undefined or the active function object, throw a TypeError exception.
  if (NewTarget instanceof UndefinedValue) {
    return surroundingAgent.Throw('TypeError', 'ConstructorNonCallable', this);
  }
  if (NewTarget === surroundingAgent.activeFunctionObject) {
    return surroundingAgent.Throw('TypeError', 'CannotConstructAbstractFunction', NewTarget);
  }

  // 2. Return ? OrdinaryCreateFromConstructor(NewTarget, "%Iterator.prototype%").
  return Q(yield* OrdinaryCreateFromConstructor(NewTarget, '%Iterator.prototype%'));
}

/** https://tc39.es/ecma262/#sec-iterator.from */
function* Iterator_from([O = Value.undefined]: Arguments): ValueEvaluator {
  // 1. Let iteratorRecord be ? GetIteratorFlattenable(O, iterate-string-primitives).
  const iteratorRecord = Q(yield* GetIteratorFlattenable(O, 'iterate-string-primitives'));

  // 2. Let hasInstance be ? OrdinaryHasInstance(%Iterator%, iteratorRecord.[[Iterator]]).
  const hasInstance: BooleanValue = Q(yield* OrdinaryHasInstance(surroundingAgent.intrinsic('%Iterator%'), iteratorRecord.Iterator));
  // 3. If hasInstance is true, then
  if (hasInstance === Value.true) {
    // a. Return iteratorRecord.[[Iterator]].
    return iteratorRecord.Iterator;
  }

  // 4. Let wrapper be OrdinaryObjectCreate(%WrapForValidIteratorPrototype%, « [[Iterated]] »).
  const wrapper = OrdinaryObjectCreate(
    surroundingAgent.intrinsic('%WrapForValidIteratorPrototype%'),
    ['Iterated'],
  ) as Mutable<IteratorObject>;
  // 5. Set wrapper.[[Iterated]] to iteratorRecord.
  wrapper.Iterated = iteratorRecord;
  // 6. Return wrapper.
  return wrapper;
}

/** https://tc39.es/ecma262/#sec-iterator.concat */
function* Iterator_concat(items: Arguments): ValueEvaluator {
  const iterables: { OpenMethod: FunctionObject, Iterable: ObjectValue }[] = [];
  for (const item of items.values()) {
    if (!(item instanceof ObjectValue)) {
      return surroundingAgent.Throw('TypeError', 'NotAnObject', item);
    }
    const method = Q(yield* GetMethod(item, wellKnownSymbols.iterator));
    if (method instanceof UndefinedValue) {
      return surroundingAgent.Throw('TypeError', 'NotIterable', item);
    }
    iterables.push({ OpenMethod: method, Iterable: item });
  }
  const gen = CreateIteratorFromClosure(function* Iterator_concat(): YieldEvaluator {
    for (const iterable of iterables) {
      const iter = Q(yield* Call(iterable.OpenMethod, iterable.Iterable));
      if (!(iter instanceof ObjectValue)) {
        return surroundingAgent.Throw('TypeError', 'NotIterable', iter);
      }
      const iteratorRecord = Q(yield* GetIteratorDirect(iter));
      let innerAlive = true;
      while (innerAlive) {
        const innerValue = Q(yield* IteratorStepValue(iteratorRecord));
        if (innerValue === 'done') {
          innerAlive = false;
        } else {
          const completion = yield* Yield(innerValue);
          if (completion instanceof AbruptCompletion) {
            return Q(yield* IteratorClose(iteratorRecord, completion));
          }
        }
      }
    }
    return Value.undefined;
  }, Value('Iterator Helper'), surroundingAgent.intrinsic('%IteratorHelperPrototype%'), ['UnderlyingIterators']);
  gen.UnderlyingIterators = [];
  return gen;
}

export function bootstrapIterator(realmRec: Realm) {
  const cons = bootstrapConstructor(realmRec, IteratorConstructor, 'Iterator', 0, realmRec.Intrinsics['%Iterator.prototype%'], [
    ['from', Iterator_from, 1],
    ['concat', Iterator_concat, 0],
  ]);

  realmRec.Intrinsics['%Iterator%'] = cons;
}