EV and subst (was Re: [Maxima] Mock-up html...)

--- Richard Fateman  wrote:

> I'm not proposing to remove the EV command.  It is just that
> some simple uses of it, say to replace x by 3,  done by
> ev(expression, x=3)
> 
> or
>    expression, x=3
> 
> are probably more clearly thought of, and computed as, substitutions.

Agreed.  But then doesn't that make subst basically a subset of the ev
command?  In principle, I don't see any problem with people using ev
for subst the way they use integrate instead of calling the specific
routines, although I suppose I'm missing something.  
 
> ev(expression, somethingflag=true)    is not a substitution, but
> as you say, sometehing having to do with an environment.
> 
> Every system makes a hash of this.  Rules in Mathematica,
> random flags in Maple and Macsyma.

So basically, your complaint with ev is that it is poorly done and used
where subst would be more expressive as a command for what is being
done?  (I guess I'd better go review some of those old ev discussions
in the archives.)

> > But I think the whole business of
> > ev, subst, ratsubst, whatever the part commands are, etc. should be
> > written up (probably as its own chapter) and clearly explained,
> > defined, measured, whatever.  

I still think we need a good chapter (at least) explaining all the ins
and outs of this stuff.  IIRC, the Macsyma Inc. manual devotes a full
chapter to it, as well.

CY


		
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