Difference between substitution and evaluation

I think the distinction should be made, to the extent
possible, among these:

evaluation  (meval)
simplification  (simplifya)
substitution    ($subst ?)

This was never very clear when we were writing Macsyma,
so I'm not sure that it can be made clear after the fact.

sin(0) simplifies to 0.
sin(0.0) probably evaluates to 0.0

substitution is much simpler.  If evaluation could be
explained as substitution, that would be nice. I doubt it..


Robert Dodier wrote:

> --- Wolfgang Jenkner <wjenkner@inode.at> wrote:
> 
> 
>>Robert Dodier <robert_dodier@yahoo.com> writes:
>>
>>
>>>If it [evaluation understood as kind of substitution] helps we can
>>>restrict consideration to meval instead of considering ev in all
>>>its glory.
> 
> 
> Sorry, I wasn't clear. "It" refers to "restrict consideration 
> to meval". What I meant was, if it is too complicated and confusing 
> to discuss ev, let's discuss meval. On further reflection it's
> become clear that ev is just irrelevant. Sorry for dragging
> in this red herring.
> 
> Now that I have an opportunity to clarify -- I guess what
> I really want to compare to substitution is whatever part
> of the Maxima command loop is called "evaluation". Looking
> at src/macsys.lisp in 'continue', it appears that is
> effectively meval. (continue -> toplevel-macsyma-eval -> meval*
> -> meval.)
> 
> Thanks for your help,
> Robert Dodier
> 
> 
> 		
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