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LibJS: Implement Iterator.prototype.reduce
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3 changed files with 196 additions and 0 deletions
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@ -35,6 +35,7 @@ ThrowCompletionOr<void> IteratorPrototype::initialize(Realm& realm)
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define_native_function(realm, vm.names.take, take, 1, attr);
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define_native_function(realm, vm.names.drop, drop, 1, attr);
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define_native_function(realm, vm.names.flatMap, flat_map, 1, attr);
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define_native_function(realm, vm.names.reduce, reduce, 1, attr);
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return {};
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}
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@ -445,4 +446,74 @@ JS_DEFINE_NATIVE_FUNCTION(IteratorPrototype::flat_map)
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return result;
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}
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// 3.1.3.7 Iterator.prototype.reduce ( reducer [ , initialValue ] ), https://tc39.es/proposal-iterator-helpers/#sec-iteratorprototype.reduce
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JS_DEFINE_NATIVE_FUNCTION(IteratorPrototype::reduce)
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{
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auto reducer = vm.argument(0);
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// 1. Let O be the this value.
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// 2. If O is not an Object, throw a TypeError exception.
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auto object = TRY(this_object(vm));
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// 3. If IsCallable(reducer) is false, throw a TypeError exception.
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if (!reducer.is_function())
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return vm.throw_completion<TypeError>(ErrorType::NotAFunction, "reducer"sv);
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// 4. Let iterated be ? GetIteratorDirect(O).
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auto iterated = TRY(get_iterator_direct(vm, object));
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Value accumulator;
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size_t counter = 0;
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// 5. If initialValue is not present, then
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if (vm.argument_count() < 2) {
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// a. Let next be ? IteratorStep(iterated).
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auto next = TRY(iterator_step(vm, iterated));
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// b. If next is false, throw a TypeError exception.
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if (!next)
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return vm.throw_completion<TypeError>(ErrorType::ReduceNoInitial);
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// c. Let accumulator be ? IteratorValue(next).
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accumulator = TRY(iterator_value(vm, *next));
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// d. Let counter be 1.
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counter = 1;
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}
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// 6. Else,
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else {
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// a. Let accumulator be initialValue.
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accumulator = vm.argument(1);
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// b. Let counter be 0.
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counter = 0;
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}
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// 7. Repeat,
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while (true) {
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// a. Let next be ? IteratorStep(iterated).
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auto next = TRY(iterator_step(vm, iterated));
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// b. If next is false, return accumulator.
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if (!next)
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return accumulator;
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// c. Let value be ? IteratorValue(next).
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auto value = TRY(iterator_value(vm, *next));
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// d. Let result be Completion(Call(reducer, undefined, « accumulator, value, 𝔽(counter) »)).
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auto result = call(vm, reducer.as_function(), js_undefined(), accumulator, value, Value { counter });
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// e. IfAbruptCloseIterator(result, iterated).
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if (result.is_error())
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return *TRY(iterator_close(vm, iterated, result.release_error()));
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// f. Set accumulator to result.[[Value]].
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accumulator = result.release_value();
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// g. Set counter to counter + 1.
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++counter;
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}
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}
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}
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@ -27,6 +27,7 @@ private:
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JS_DECLARE_NATIVE_FUNCTION(take);
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JS_DECLARE_NATIVE_FUNCTION(drop);
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JS_DECLARE_NATIVE_FUNCTION(flat_map);
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JS_DECLARE_NATIVE_FUNCTION(reduce);
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};
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}
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