On Thu, Jun 21, 2012 at 11:23 AM, Brendan Eich <[email protected]> wrote:
> John Tamplin wrote: > >> So do you have to do it by treating the ?. operator as a standalone? >> > Not sure what you mean here -- "standalone ?" (with an English-langauge ? > implied after in your sentence? ;-)? > > Or something else that amounts to a concealed Reference or Nil-value-proxy > expression? > > Just talking spec here: as Allen mentioned, ECMA-262 specifies semantics > by evaluating productions in a mostly-LR(1) grammar, so member and call > expressions (left-associative) have to result in some kind of > (spec-internal or language-external) value. > > Thus foo?.bar.baz.quux is really (((foo?.bar).baz).quux). Yes, and I am suggesting during parsing it gets treated as: (((foo?.bar)?.baz)?.quux) because we saw a ?. operator earlier in the expression. That way you don't have to get the Coffeescript behavior by introducing some fake object or a MaybeReference, and you just implement the ?. operator as always returning the LHS if it is null/undef. > Indeed one can translate when parsing. CoffeeScript does this, with some > separate passes for its other purposes (implicitly declared variables, > indentation-based block structure, etc.). > > The ES specs can't do this, though, not without a total rewrite. I realize it would be changes, but then so would adding a MaybeReference. Just thought I would bring it up. -- John A. Tamplin Software Engineer (GWT), Google
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