Expression-scoped pragmas

[lth]

Motivation: The number pragmas are our main mechanism for invoking a particular kind of operator, particularly for int and uint. But they are block scoped only -- so code that wants to invoke two different kinds of operators (say, code adding the elements of an array of generic numbers) must structure their code somewhat elaborately with temporaries and multiple blocks.

It would be simple for us to add expression-scoped number pragmas, and I think we should.

The syntax would be:

let (use <pragma>, ...) expression

Example:

let (use int) a+b

is exactly the same as

(function () { use int; return a+b })()

Some other pragmas could usefully be adopted under this umbrella: namespace, rounding, and precision for sure:

let (use namespace intrinsic, decimal, precision=20) a+b

The exact set of allowed pragmas: TBD.

[lth]

See longer discussion with samples here: https://intranet.mozilla.org/ECMA/wiki/doku.php?id=discussion:numbers. Please annotate that page, do not comment here.

[jeffdyer]

Accepted at Yahoo! meeting. Moving to RI bug.

[lth]

Not obvious this is needed any more, since the number pragmas have been removed. Reverting to proposal stage for reconsideration at future meeting.

[lth]

Specifically, I propose that we remove expression-scoped pragmas from the language.