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Editorial: enable built-in async and sync generator functions to be specified #1665

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Editorial: enable built-in async and sync generator functions to be specified #1665

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5c30982
Editorial: enable built-in async and sync generator functions to be s…
devsnek Aug 11, 2019
6a165b4
add prelude and body, fix [[Construct]]
devsnek Aug 12, 2019
b9b079b
set correct prototype in CreateBuiltinFunction
devsnek Aug 12, 2019
10cf076
add normal async functions
devsnek Aug 12, 2019
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123 changes: 111 additions & 12 deletions spec.html
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Expand Up @@ -371,6 +371,16 @@ <h1>built-in function</h1>
</emu-note>
</emu-clause>

<emu-clause id="sec-built-in-generator-function">
<h1>built-in generator function</h1>
<p>built-in object that is a generator function</p>
</emu-clause>

<emu-clause id="sec-built-in-async-generator-function">
<h1>built-in async generator function</h1>
<p>built-in object that is an async generator function</p>
</emu-clause>

<emu-clause id="sec-property">
<h1>property</h1>
<p>part of an object that associates a key (either a String value or a Symbol value) and a value</p>
Expand Down Expand Up @@ -3138,6 +3148,29 @@ <h1>Await Rejected Functions</h1>
</emu-clause>
</emu-clause>

<emu-clause id="yield" aoid="Yield">
<h1>Yield</h1>

<p>Algorithm steps that say</p>

<emu-alg>
1. Let _completion_ be Yield(_value_).
</emu-alg>

<p>mean the same thing as:</p>

<emu-alg>
1. Let _generatorKind_ be ! GetGeneratorKind().
1. If _generatorKind_ is ~async~, then
1. Let _completion_ be AsyncGeneratorYield(_value_).
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1. Otherwise,
1. Let _completion_ be GeneratorYield(CreateIterResultObject(_value_, *false*)).
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</emu-alg>

<p>where all variables in the above steps, with the exception of _completion_, are ephemeral and visible only in the steps pertaining to Yield.</p>

</emu-clause>

<emu-clause id="sec-normalcompletion" aoid="NormalCompletion">
<h1>NormalCompletion</h1>
<p>The abstract operation NormalCompletion with a single _argument_, such as:</p>
Expand Down Expand Up @@ -7793,9 +7826,63 @@ <h1>[[Call]] ( _thisArgument_, _argumentsList_ )</h1>
1. Set the ScriptOrModule of _calleeContext_ to _F_.[[ScriptOrModule]].
1. Perform any necessary implementation-defined initialization of _calleeContext_.
1. Push _calleeContext_ onto the execution context stack; _calleeContext_ is now the running execution context.
1. Let _result_ be the Completion Record that is the result of evaluating _F_ in an implementation-defined manner that conforms to the specification of _F_. _thisArgument_ is the *this* value, _argumentsList_ provides the named parameters, and the NewTarget value is *undefined*.
1. Remove _calleeContext_ from the execution context stack and restore _callerContext_ as the running execution context.
1. Return _result_.
1. If _F_ is a built-in async function, then
1. Let _asyncContext_ be a copy of _calleeContext_.
1. Set the code evaluation state of _asyncContext_ such that when evaluation is resumed for that execution context the following steps will be performed:
1. Let _result_ be the Completion Record that is the result of evaluating _F_ in an implementation-defined manner that confirms to the specification of _F_. _thisArgument_ is the *this* value, _argumentsList_ provides the named parameters, and NewTarget is *undefined*.
1. Remove _asyncContext_ from the execution context stack and restore the execution context that is at the top of the execution context stack as the running execution context.
1. If _result_ is an abrupt completion, then
1. Perform ! Call(_promiseCapability_.[[Reject]], *undefined*, &laquo; _result.[[Value]] &raquo;).
1. Else,
1. Perform ! Call(_promiseCapability_.[[Resolve]], *undefined*, &laquo; _result_.[[Value]] &raquo;).
1. Return.
1. Push _asyncContext_ onto the execution context stack; _asyncContext_ is now the running execution context.
1. Resume the suspended evaluation of _asyncContext_. Let _result_ be the value returned by the resumed computation.
1. Assert: _calleeContext_ is the running execution context.
1. Assert: _result_ is a normal completion with a value of *undefined*.
1. Remove _calleeContext_ from the execution context stack and restore _callerContext_ as the running execution context.
1. Return _promiseCapability_.[[Promise]].
1. If _F_ is a built-in generator function, then
1. Let _result_ be the completion record that is the result of evaluating the prelude steps of _F_ in an implementation-defined manner that conforms to the specification of _F_. _thisArgument_ is the *this* value, _argumentsList_ provides the named parameters, and NewTarget is *undefined*.
1. If _result_ is an abrupt completion, return _result_.
1. Let _generator_ be ? OrdinaryCreateFromConstructor(_F_, "%GeneratorPrototype%", « [[GeneratorState]], [[GeneratorContext]] »).
1. Set the Generator component of _calleeContext_ to _generator_.
1. Set _generator_.[[GeneratorState]] to *"suspendedStart"*.
1. Set the code evaluation state of _calleeContext_ such that when evaluation is resumed for that execution context the following steps will be performed:
1. Let _result_ be the Completion Record that is the result of evaluating the body steps of _F_ in an implementaion-defined manner that confirms to the specification of _F_. _thisArgument_ is the *this* value, _argumentsList_ provides the named parameters, and NewTarget is *undefined*.
1. Remove _calleeContext_ from the execution context stack and restore the execution context that is at the top of the execution context stack as the running execution context.
1. Set _generator_.[[GeneratorState]] to *"completed"*.
1. If _result_ is an abrupt completion, then
1. Return _result_.
1. Else,
1. Let _resultValue_ be _result_.[[Value]].
1. Return CreateIterResultObject(_resultValue_, *true*).
1. Remove _calleeContext_ from the execution context stack and restore _callerContext_ as the running execution context.
1. Return _generator_.
1. Else if _F_ is a built-in async generator function, then
1. Let _result_ be the completion record that is the result of evaluating the prelude steps of _F_ in an implementation-defined manner that conforms to the specification of _F_. _thisArgument_ is the *this* value, _argumentsList_ provides the named parameters, and NewTarget is *undefined*.
1. If _result_ is an abrupt completion, return _result_.
1. Let _generator_ be ? OrdinaryCreateFromConstructor(_F_, "%AsyncGeneratorPrototype%", « [[AsyncGeneratorState]], [[AsyncGeneratorContext]], [[AsyncGeneratorQueue]] »).
1. Set the Generator component of _calleeContext_ to _generator_.
1. Set _generator_.[[AsyncGeneratorContext]] to _calleeContext_.
1. Set _generator_.[[AsyncGeneratorState]] to *"suspendedStart"*.
1. Set _generator_.[[AsyncGeneratorQueue]] to a new empty List.
1. Set the code evaluation state of _calleeContext_ such that when evaluation is resumed for that execution context the following steps are performed:
1. Let _result_ be the Completion Record that is the result of evaluating the body steps of _F_ in an implementaion-defined manner that confirms to the specification of _F_. _thisArgument_ is the *this* value, _argumentsList_ provides the named parameters, and NewTarget is *undefined*.
1. Remove _calleeContext_ from the execution context stack and restore the execution context that is at the top of the execution context stack as the running execution context.
1. Set _generator_.[[AsyncGeneratorState]] to *"completed"*.
1. If _result_ is an abrupt completion, then
1. Let _resultValue_ be _result_.[[Value]].
1. Return ! AsyncGeneratorReject(_generator_, _resultValue_).
1. Else,
1. Set _resultValue_ to _result_.[[Value]].
1. Return ! AsyncGeneratorResolve(_generator_, _resultValue_).
1. Remove _calleeContext_ from the execution context stack and restore _callerContext_ as the running execution context.
1. Return _generator_.
1. Otherwise,
1. Let _result_ be the Completion Record that is the result of evaluating _F_ in an implementation-defined manner that conforms to the specification of _F_. _thisArgument_ is the *this* value, _argumentsList_ provides the named parameters, and the NewTarget value is *undefined*.
1. Remove _calleeContext_ from the execution context stack and restore _callerContext_ as the running execution context.
1. Return _result_.
</emu-alg>
<emu-note>
<p>When _calleeContext_ is removed from the execution context stack it must not be destroyed if it has been suspended and retained by an accessible generator object for later resumption.</p>
Expand All @@ -7804,9 +7891,21 @@ <h1>[[Call]] ( _thisArgument_, _argumentsList_ )</h1>

<emu-clause id="sec-built-in-function-objects-construct-argumentslist-newtarget">
<h1>[[Construct]] ( _argumentsList_, _newTarget_ )</h1>
<p>The [[Construct]] internal method for built-in function object _F_ is called with parameters _argumentsList_ and _newTarget_. The steps performed are the same as [[Call]] (see <emu-xref href="#sec-built-in-function-objects-call-thisargument-argumentslist"></emu-xref>) except that step 10 is replaced by:</p>
<p>The [[Construct]] internal method for built-in function object _F_ is called with parameters _argumentsList_ and _newTarget_.</p>
<emu-alg>
10. Let _result_ be the Completion Record that is the result of evaluating _F_ in an implementation-defined manner that conforms to the specification of _F_. The *this* value is uninitialized, _argumentsList_ provides the named parameters, and _newTarget_ provides the NewTarget value.
1. If _F_ is a built-in async function, built-in generator function, or a built-in async generator function, throw a *TypeError* exception.
1. Let _callerContext_ be the running execution context.
1. If _callerContext_ is not already suspended, suspend _callerContext_.
1. Let _calleeContext_ be a new execution context.
1. Set the Function of _calleeContext_ to _F_.
1. Let _calleeRealm_ be _F_.[[Realm]].
1. Set the Realm of _calleeContext_ to _calleeRealm_.
1. Set the ScriptOrModule of _calleeContext_ to _F_.[[ScriptOrModule]].
1. Perform any necessary implementation-defined initialization of _calleeContext_.
1. Push _calleeContext_ onto the execution context stack; _calleeContext_ is now the running execution context.
1. Let _result_ be the Completion Record that is the result of evaluating _F_ in an implementation-defined manner that conforms to the specification of _F_. The *this* value is uninitialized, _argumentsList_ provides the named parameters, and _newTarget_ provides the NewTarget value.
1. Remove _calleeContext_ from the execution context stack and restore _callerContext_ as the running execution context.
1. Return _result_.
</emu-alg>
</emu-clause>

Expand All @@ -7817,7 +7916,11 @@ <h1>CreateBuiltinFunction ( _steps_, _internalSlotsList_ [ , _realm_ [ , _protot
1. Assert: _steps_ is either a set of algorithm steps or other definition of a function's behaviour provided in this specification.
1. If _realm_ is not present, set _realm_ to the current Realm Record.
1. Assert: _realm_ is a Realm Record.
1. If _prototype_ is not present, set _prototype_ to _realm_.[[Intrinsics]].[[%Function.prototype%]].
1. If _prototype_ is not present, then
1. If _steps_ refers to the steps of a built-in async function, set _prototype_ to _realm_.[[Intrinsics]].[[%AsyncFunction.prototype%]].
1. Else if _steps_ refers to the steps of a built-in generator function, set _prototype_ to _realm_.[[Intrinsics]].[[%Generator%]].
1. Else if _steps_ refers to the steps of a built-in async generator function, set _prototype_ to _realm_.[[Intrinsics]].[[%AsyncGenerator%]].
1. Otherwise, set _prototype_ to _realm_.[[Intrinsics]].[[%Function.prototype%]].
1. Let _func_ be a new built-in function object that when called performs the action described by _steps_. The new function object has internal slots whose names are the elements of _internalSlotsList_.
1. Set _func_.[[Realm]] to _realm_.
1. Set _func_.[[Prototype]] to _prototype_.
Expand Down Expand Up @@ -19337,17 +19440,13 @@ <h1>Runtime Semantics: Evaluation</h1>
</emu-note>
<emu-grammar>YieldExpression : `yield`</emu-grammar>
<emu-alg>
1. Let _generatorKind_ be ! GetGeneratorKind().
1. If _generatorKind_ is ~async~, then return ? AsyncGeneratorYield(*undefined*).
1. Otherwise, return ? GeneratorYield(CreateIterResultObject(*undefined*, *false*)).
1. Return Yield(*undefined*).
</emu-alg>
<emu-grammar>YieldExpression : `yield` AssignmentExpression</emu-grammar>
<emu-alg>
1. Let _generatorKind_ be ! GetGeneratorKind().
1. Let _exprRef_ be the result of evaluating |AssignmentExpression|.
1. Let _value_ be ? GetValue(_exprRef_).
1. If _generatorKind_ is ~async~, then return ? AsyncGeneratorYield(_value_).
1. Otherwise, return ? GeneratorYield(CreateIterResultObject(_value_, *false*)).
1. Return Yield(_value_).
</emu-alg>
<emu-grammar>YieldExpression : `yield` `*` AssignmentExpression</emu-grammar>
<emu-alg>
Expand Down