April 10 2014 Meeting Notes

C. Scott Ananian ecmascript at cscott.net
Wed Apr 30 07:33:45 PDT 2014

On Tue, Apr 29, 2014 at 7:47 PM, David Herman <dherman at mozilla.com> wrote:

> Promised you a reply to this one, sorry -- I'm not comfortable with this
> restriction. It violates my Schemer's intuition [1]. In particular it
> creates a number of refactoring hazards: (1) add some try/finally

> [1] "Programming languages should be designed not by piling feature on top
> of feature, but by removing the weaknesses and restrictions that make
> additional features appear necessary."

In support of your intuition, here is how you'd implement Domenic's `using`
construct (or `for-using`) using the improved `for-of` (pardon the
mostly-ES5 syntax):

var using = function*(o) {
   try {
      yield o;
   } finally { o.close(); }

for (var file of using(open("filename"))) {
   process(file.read()); // or whatever

- All three of .next, .throw, and .return should take an optional argument.

Calling `.throw()` with no arguments is surprising, but the result
(presumably throwing `undefined`) is consistent with the rest of the
language.  I like the orthogonality of your proposal.
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