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Normative: Ban |> await #73

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24 changes: 1 addition & 23 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -78,29 +78,7 @@ As you can see, because the pipe operator always pipes a single result value, it

### Use of `await`

The pipeline operator allows a `Promise` to be `await`ed as follows:

```js
promise |> await
```

which is the equivalent of

```js
await promise
```

This is to allow you to `await` the result of an asynchronous function and pass it to the next function from within a function pipeline, as follows:

```js
const userAge = userId |> fetchUserById |> await |> getAgeFromUser
```

which is the equivalent of

```js
const userAge = getAgeFromUser(await fetchUserById(userId))
```
The pipeline operator does not have any special integration with async/await in its initial version, due to [issues](https://github.com/tc39/proposal-pipeline-operator/issues/66) with various alternatives discussed. To leave space for future additions to integrate await support, the not-very-useful sequence `|> await` (which would otherwise await a function, not the result of calling a function) is a SyntaxError.

### Usage with Function.prototype.papp

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27 changes: 21 additions & 6 deletions spec.html
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Expand Up @@ -34,20 +34,21 @@ <h1>Syntax</h1>
<ins>
PipelineExpression[In, Yield, Await] :
LogicalORExpression[?In, ?Yield, ?Await]
PipelineExpression[?In, ?Yield, ?Await] `|>` LogicalORExpression[?In, ?Yield, ?Await]
[~Await] PipelineExpression[?In, ?Yield, ?Await] `|>` LogicalORExpression[?In, ?Yield, ?Await]
[+Await] PipelineExpression[?In, ?Yield, ?Await] `|>` [lookahead &lt;! {`await`}] LogicalORExpression[?In, ?Yield, ?Await]
</ins>
</emu-grammar>
</emu-clause>

<emu-clause id=sec-pipeline-semantics>
<h1>Semantics</h1>
<emu-clause id=sec-pipeline-evaluation>
<h1>Runtime Semantics: Evaluation</h1>
<emu-grammar>PipelineExpression : PipelineExpression '|>` LogicalORExpression</emu-grammar>
<emu-clause id="sec-pipeline-evaluate">
<h1>Runtime Semantics: PipelineEvaluate</h1>
PipelineEvaluate for _lhs_ and _rhs_ performs the following steps:
<emu-alg>
1. Let _argRef_ be the result of evaluating |PipelineExpression|.
1. Let _argRef_ be the result of evaluating _lhs_.
1. Let _arg_ be ? GetValue(_argRef_).
1. Let _funcRef_ be the result of evaluating |LogicalORExpression|.
1. Let _funcRef_ be the result of evaluating _rhs_.
1. Let _func_ be ? GetValue(_funcRef_).
1. If Type(_funcRef_) is Reference, then
1. If IsPropertyReference(_funcRef_) is *true*, then
Expand All @@ -70,6 +71,20 @@ <h1>Runtime Semantics: Evaluation</h1>
<emu-note>All calls to eval from a pipeline operator are indirect eval calls.</emu-note>
<emu-note type="editor">This definition is somewhat duplicated from the definition of evaluating CallExpression; when merging with the main specification, a refactoring will be done to de-duplicate it.</emu-note>
</emu-clause>


<emu-clause id=sec-pipeline-evaluation>
<h1>Runtime Semantics: Evaluation</h1>
<emu-grammar>PipelineExpression : PipelineExpression `|>` LogicalORExpression</emu-grammar>
<emu-alg>
1. Let _result_ be the result of PipelineEvaluate for |PipelineExpression| and |LogicalORExpression|.
1. Return _result_.
</emu-alg>
<emu-grammar>PipelineExpression : LogicalORExpression</emu-grammar>
<emu-alg>
1. Return the result of evaluating |LogicalORExpression|.
</emu-alg>
</emu-clause>
<emu-clause id=sec-pipeline-has-call-in-tail-position>
<h1>Static Semantics: HasCallInTailPosition</h1>
<emu-grammar>PipelineExpression : PipelineExpression '|>` LogicalORExpression</emu-grammar>
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