Re: Statistics on Macsyma use of SUBST

[Kent M. Pitman <KMP at MIT-MC>]

A by-hand survey says that things break down this way:

 77 substitutions for symbols
  4 substitutions of NIL for NIL (2 macros + 2 isolated occurrences)
  1 substitution for (CONS ...) 
  1 substitution of 1 for 0

Many of the substitutions for symbols do break data abstraction, as GJC
mentions, and of those that don't, many are just places where backquote
would have been used had it been available at the time of the code's
development (eg, JM's SIN has at least one such occurrence). 

This data is based on what I believe are the expectations on things. eg,
(SUBST foo var x) or (SUBST var v x) were assumed to be substitutions for
symbols.

I suspect, really, that SUBST is too powerful for most of our applications.
We have been screwed more than once by SUBST poking around in parts of
expressions that we should never have allowed it into... ('we' here meaning
the Mathlab group). We probably oughtn't be using it as much as we do...

-kmp