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Re: Rvalue given() blocks

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Rafael Garcia-Suarez
July 20, 2009 02:34
Re: Rvalue given() blocks
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2009/7/20 Vincent Pit <>:
> Just as the title says, this patch makes given() blocks return values,
> with the following rules :
> - if an explicit break is encountered, return an empty list ;
> - if a when/default clause is true (and doesn't contain an explicit
> break), return the value of the last evaluated expression of the block ;
> - if all conditions were false, return the value of the last evaluated
> expression of the block.
> I've also made when/default not return anything (unlike 'if' and
> 'unless' which returns the value of the condition).
> Regarding the implementation, I added 'switch' to the 'term' rule. This
> made the YYLAST value increase a lot :
> -#define YYLAST   2061
> +#define YYLAST   2446
> I'm not a bison specialist, so I'd like to know if there isn't some kind
> of heavy penalty hidden there.
> Then I made scalar()/list() correctly propagate into given/when OPs.
> There's very little run-time changes. pp_leavegiven() was just taught to
> correctly set the stack pointer. It also mimics pp_leavetry() to make
> sure that all the stack elements are correctly tainted/mortalized.

This is extremely neat.
However by looking at the perly.y part of the patch (I haven't looked
at the other ones yet) I see that you add switch as a derivation for
the term rule, but switch can begin with a label. And terms don't.

I'd rather have a new rule
switch : label given;
and add given to term.

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