From: Dan Sugalski <dan@...>
Date: 2003-01-07T01:11:05+09:00
Subject: Re: Compile time constant folding?

At 12:24 AM +0900 1/7/03, Mark Probert wrote:
>At 10:08 AM 1/6/2003 +0900, Dan wrote:
>>At 9:19 AM +0900 1/6/03, Mark Probert wrote:
>>>Dan Sugalski wrote in comp.lang.ruby:
>>>>
>>>>  Is it valid to do compile-time constant folding as an optimization?
>>>
>>>IMO, the POLS wouldn't be breeched if this were to happen.
>>
>>I can see it going either way--the interpreter could do what it's 
>>doing on purpose, or because the optimization just never was done. 
>>(Or that it wasn't ever really thought about)
>>
>>It's not like this is expensive in the simple case, but when you do 
>>something like:
>>
>>    (1 / sin(2.3)) * log(4)
>>
>>in a loop, well, that can add up pretty quickly.
>
>I say: 15.002 --> optimise.  ;-)
>Given that we know the base, and it is also constant.
>
>This is the thing for me.  Constants are, well, constants.

Maybe, but add isn't necessarily add--it's the actions that need to 
be taken rather than the values themselves that are in question. If 
someone redefines + to be unconditional string concatenation, or 
wedges in logging logic, you may well want that to happen at runtime 
with the constant expression.
-- 
                                         Dan

--------------------------------------"it's like this"-------------------
Dan Sugalski                          even samurai
dan@sidhe.org                         have teddy bears and even
                                       teddy bears get drunk