[Python-ideas] for/else syntax

[Georg Brandl]

Yuvgoog Greenle schrieb:
> Ok, in theory, it's possible to flag a boolean after a for/while when
> compiling, but I think the "special syntax" option might be simpler to
> implement. So let's talk grammar...
> 
> The old grammar was:
> 
> while_stmt ::=  "while" expression ":" suite
>                 ["else" ":" suite]
> 
> for_stmt ::=  "for" target_list "in" expression_list ":" suite
>               ["else" ":" suite]
> 
> 
> And the new one I propose looks like this:
> 
> while_stmt ::=  "while" expression ":" suite
>                 ["if" expression ":" suite]
> 
> for_stmt ::=  "for" target_list "in" expression_list ":" suite
>               ["if" expression ":" suite]
> 
> 
> The "if" expression would be evaluated regularly but would have a
> magic boolean "break" that exists only in the if statement's
> expression eval. Note a few things:
> 1. the "if" would have been evaluated either way after the loop
> (exceptions/returns aside).
> 2. the only thing that's changed is the existence of the magic boolean "break".
> 3. You don't have to use it as the old "for...else" but you can and
> it's perfectly readable.
> 
> I'm no expert on the compiler, but I have a strong feeling this is doable.

Sure, almost any language change is doable if you bend over backwards far
enough and break all rules of consistency.

Georg

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