From: "David A. Black" <dblack@...>
Date: 2005-11-22T22:11:47+09:00
Subject: Re: semenatics of if/unless/while statement modifiers

Hi --

On Tue, 22 Nov 2005, Stefan Kaes wrote:

> Yukihiro Matsumoto wrote:
>
>> Hi,
>> 
>> In message "Re: semenatics of if/unless/while statement modifiers"
>>    on Tue, 22 Nov 2005 09:54:46 +0900, Stefan Kaes <skaes@gmx.net> writes:
>> 
>> |So this behaviour is caused by intermingling parsing with semantic 
>> |analysis. Much like forward procedure declarations were required for old 
>> |Pascal compilers.
>> 
>> I believe it's a strict application of the "local variables should be
>> assigned first" rule.  Not a compromise for the compiler.
>> 
> It is definitely a compiler issue. Just like the recent discussion of the 
> syntax for block parameters is only a compiler issue.
>
> In both forms, the v=expr gets evaluated first. So during evaluation, the 
> assignment v=expr is always seen first, which means to me, a local variable 
> gets created and assigned in the current binding. Any decent formal semantics 
> writer would  like to treat both forms identically too, simply by stating 
> that "expr1 if expr2" is equivalent to "if expr2 then expr1" end.
>
> If the resolution of local variable assignment vs. function call were 
> implemented as a second pass on the abstract syntax tree or using some form 
> of back patching, there would be no difference between the 2 forms to begin 
> with.

What would you want to happen here?

   def x
     puts "method x"
   end

   x if x = 1   # method x
   puts x       # 1


David

-- 
David A. Black
dblack@wobblini.net