On Thu, Jul 11, 2013 at 5:08 PM, Brendan Eich <[email protected]> wrote:
>
> Very messy, and primordial JS (the "Mocha" interpreter) violated ECMA-262
> Edition 1 on order of evaluation, e.g., o[x] = ++x where the RHS ++x must be
> evaluated *after* the Reference o[x] is evaluated. Fixing this prior to
> compiling to a parse tree required code buffering and reordering, just as
> the for loops (both of 'em) can.
>
> Again, this goes back to the dawn of JS. We're not making it any worse. I
> don't see finite lookahead helping in general for any of these cases, BTW.
>
> /be
Compiling this
arr[x] = ++x;
does not require complete AST support as far as I can tell.
Consider this:
Some hypothetical bytecode:
PUSH arr;
PUSH x;
--
<RHS code> -> VAL in accumulator register
--
SETVI; // stack[TOP-1] <- arr
// stack[TOP] <- x, index, initial value of x
// accum <- x, final RHS value, x after increment
DROP2;
// accum here contains x value after increment - result
// of the assignment expression.
So that can be compiled to stack machine strictly in order
it is defined.
Or do you mean something else here?
--
Andrew Fedoniouk.
http://terrainformatica.com
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