ES6 feature: Generator: Tracking Issue

[ariya]

Syntax:

Per Rev 32 (Feb 2, 2015) of the draft spec, the relevant grammar is on Section 14.4 Generator Function Definitions:

GeneratorMethod[Yield] :
    * PropertyName[?Yield] ( StrictFormalParameters[Yield,GeneratorParameter] )  { GeneratorBody[Yield]  }

GeneratorDeclaration[Yield, Default] :
    function * BindingIdentifier[?Yield] ( FormalParameters[Yield, GeneratorParameter] ) { GeneratorBody[Yield] }
    [+Default] function * ( FormalParameters[Yield, GeneratorParameter] ) { GeneratorBody[Yield] }

GeneratorExpression :
    function * BindingIdentifier[Yield]opt ( FormalParameters[Yield,GeneratorParameter] ) { GeneratorBody[Yield] }

GeneratorBody[Yield] :
    FunctionBody[?Yield]

YieldExpression[In] :
    yield
    yield [no LineTerminator here] [Lexical goal InputElementRegExp] AssignmentExpression[?In, Yield]
    yield [no LineTerminator here] * [Lexical goal InputElementRegExp] AssignmentExpression[?In, Yield]

AssignmentExpression[In, Yield] :
    [+Yield] YieldExpression[?In]

Spec:

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-generator-function-definitions

Relevant AST interfaces (from https://github.com/estree/estree):

Functions:

extend interface Function {
    defaults: [ Expression ];
    rest: Identifier | null;
    generator: boolean;
}

interface ArrowExpression <: Function, Expression {
    type: "ArrowExpression";
    params: [ Pattern ];
    defaults: [ Expression ];
    rest: Identifier | null;
    body: BlockStatement | Expression;
    generator: boolean;
    expression: boolean;
}

YieldExpression:

interface YieldExpression <: Expression {
    type: "YieldExpression";
    argument: Expression | null;
}

See also:

• Esprima generator support from harmony branch: https://code.google.com/p/esprima/issues/detail?id=287
• V8 generator support: https://code.google.com/p/v8/issues/detail?id=2355

Remaining Tasks:

• Review V8 error messages on generator early error
• Ensure the proper handling of yield* (old issue 617)

[ariya]

@jeffmo Here's the generator tracking issue, in case you want to grab this.

[jeffmo]

David (@dhe128) mentioned he'd be interested in giving generator support a go -- so cc'ing him here for reference

[nzakas]

Was ArrowExpression vs. ArrowFunctionExpression resolved?

[jeffmo]

Hmm, well there isn't such a thing as generator arrow functions in ES6...

[nzakas]

Good point, my comment was based on the inclusion of ArrowExpression as part of the relevant AST information in the description. It seems like generator is still there so all nodes representing functions have the same properties?