ES2015 arrow functions require an empty parameter list when you don't want any parameters, eg: p.then(() => resolve()). This proposal makes it syntactically valid to omit the empty parameter list, eg: p.then(=> resolve()). The [no LineTerminator here] restriction after the ArrowParameters of ArrowFunction ensures there is no syntactic difficulty. Minor modifications are required to the grammar and a few abstract operations.
In the current async functions proposal, there is a syntactic form for async arrow functions:
async () => 1;
This might lead developers to try to use the following headless async arrow:
async => new Promise();
Unfortunately, this is a perfectly valid arrow function with one parameter named async. This may make this proposal untenable, or it might be a good reason to modify or remove async arrows from the async functions proposal.
NOTE: Non-strict functions use a separate lexical Environment Record for top-level lexical declarations so that a direct eval (see 188.8.131.52) can determine whether any var scoped declarations introduced by the eval code conflict with pre-existing top-level lexically scoped declarations. This is not needed for strict functions because a strict direct eval always places all declarations into a new Environment Record.
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