[CM] TeXmacs & S7

[bil at ccrma.Stanford.EDU]

> Why not maintain a hash table whose values are offsets into the flat 
> environment?
> Then it's a cheap branch or two on lookup to see: 1) is there a hash 
> table;
> 2) should I build one (is the env big enough, and have there been 
> enough lookups).

I call that serious overhead.  Environments come and go at an amazing
pace.  Most lookups are already immediate (do not involve a search).
In some cases (non-recursive, safe functions), I can save
the environment and reuse it, so some analysis might be acceptable.
I doubt that applies here because apparently the optimizer already
threw up its hands.

(Environments in s7 are very dynamic -- I do not currently
try to keep the env's length stored somewhere, and to get it
is nearly as bad as a linear search).