On Fri, Dec 5, 2008 at 12:39 PM, Maciej Stachowiak <[EMAIL PROTECTED]> wrote:
>
> What exactly does return from a lambda mean? Let's say I do this:
>
> function F(x) { return lambda(n) { return x + n; } }
> function G(h) { return h(1) +1; }
> var H = F(1);
> G(H);
>
> What is the value of the last expression and why?
Based on the lambda and return-to-label strawmen, It's an error. Dave
presents a desugaring of function to lambda, where each function body
is given a label at the bottom:
lambda(x0,...,xn,...$rest) {
let $THIS = thisRegister;
let arguments = makeAlias([[lambda() x1, lambda($x1) x1 = $x1],
...,
[lambda() xn, lambda($xn) xn = $xn]],
$rest);
$RETURN: { Body; void 0 }
}
'return e' without a label desugars to:
return : $RETURN e
But, from the return-to-label strawman:
"The dynamic return point associated with the label must still be live
when the return statement is invoked; otherwise it is a dynamic error,
i.e., an exception is raised."
A label is an escape continuation. Once control has returned past the
point where the continuation was captured, it's dead, and it can't be
resumed.
-Jon
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