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RFC: React Expressions with Explicit Generator Expression Semantics #99

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RFC: React Expressions with Explicit Generator Expression Semantics #99

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e2d0e4b
Update spec with jsx generation expressions
Nov 9, 2017
68a5183
Disambiguate * in JSXText
Nov 14, 2017
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14 changes: 12 additions & 2 deletions AST.md
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Original file line number Diff line number Diff line change
Expand Up @@ -47,12 +47,22 @@ interface JSXEmptyExpression <: Node {
}
```

Any expression used as attribute value or inside JSX text should is wrapped into expression container:
The expression container node contains statements with the same grammar as a generator body. Also it has a flag to indicate whether it is an expression. Any expression used as attribute value or inside JSX text should is wrapped into expression container:

```js
interface JSXExpressionContainer <: Node {
type: "JSXExpressionContainer";
expression: Expression | JSXEmptyExpression;
expression: Expression | JSXEmptyExpression | JSXBlockStatement;
isExpression: boolean;
}
```

From `BlockStatement`, this inherits `body: [ Statement ];`.

```js
interface JSXBlockStatement <: BlockStatement {
type: "JSXStatementList";
generator: boolean;
}
```

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17 changes: 16 additions & 1 deletion README.md
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Expand Up @@ -40,6 +40,7 @@ PrimaryExpression :

- JSXElement
- JSXFragment
- JSXGeneratorExpressionContainer

__Elements__

Expand Down Expand Up @@ -115,9 +116,21 @@ JSXAttributeValue :

- `"` JSXDoubleStringCharacters<sub>opt</sub> `"`
- `'` JSXSingleStringCharacters<sub>opt</sub> `'`
- `{` AssignmentExpression `}`
- JSXGeneratorExpressionContainer
- JSXElement
- JSXFragment

JSXGeneratorExpressionContainer :
- `*` `{` JSXGeneratorExpression<sub>opt</sub> `}`

JSXGeneratorExpression :
- ObjectLiteral
- FunctionExpression
- ClassExpression
- GeneratorExpression
- AsyncFunctionExpression
- FunctionBody<sub>[+Yield, ~Await, ~Return]</sub>
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@sebmarkbage sebmarkbage Nov 9, 2017 •
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FunctionBody is ambiguous since it also includes BlockStatement, FunctionDeclaration, ClassDeclaration, GeneratorExpression and AsyncFunctionDeclaration.

We need to exclude them from the list. Either by defining our own statement list explicitly, or by excluding these by some kind of lookahead.

E.g. an explicit list could look something like this:

JSXStatementList:
  JSXStatementListFirstItem StatementList[opt]

JSXStatementListFirstItem:
  LexicalDeclaration
  VariableStatement
  ExpressionStatement
  IfStatement
  BreakableStatement
  BreakStatement
  WithStatement
  LabelledStatement
  ThrowStatement
  TryStatement
  DebuggerStatement

(This also highlights the maintenance cost associated with forking the language.)

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@clemmy clemmy Nov 14, 2017 •
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Ah I see, this is a problem with the other proposal as well, and I'm not sure there's a way to lower the maintenance cost by a significant amount. Either way, we'll need to keep adding to lookaheads or JSXStatementListFirstItem for new ECMAScript features. For now I'll just go with the lookahead approach - we just can't have {, class, async, function, and do right?

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Wondering what to do for (...


JSXDoubleStringCharacters :


- JSXDoubleStringCharacter JSXDoubleStringCharacters<sub>opt</sub>
Expand Down Expand Up @@ -145,15 +158,17 @@ JSXChild :
- JSXText
- JSXElement
- JSXFragment
- JSXGeneratorExpressionContainer
- `{` JSXChildExpression<sub>opt</sub> `}`

JSXText :
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We'll need a disambiguator in JSXText for * {. For example, you can exclude * from JSXTextCharacter and explicitly allow it in JSXText for certain contexts. E.g. by a look ahead.

Note that JSXGeneratorExpressionContainer is defined in terms of two token so spaces, comments etc. are allowed between. E.g. this is still a generator:

<div>* /* hello */ { yield 1; }</div>


- JSXTextCharacter JSXText<sub>opt</sub>
- [lookahead &#8713; { `{` }] `*` JSXText<sub>opt</sub>

JSXTextCharacter :

- SourceCharacter __but not one of `{`, `<`, `>` or `}`__
- SourceCharacter __but not one of `*`, `{`, `<`, `>` or `}`__

JSXChildExpression :

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