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Re: scheme in prolog

I was about to respond to the Tim Finin / Mike Beckerle discussion
in much the same way that Ken Kahn did, so I won't bother now, except
to point out that the efficiency issue, in particular the "aggregate
update" or "copy avoidance" issue, has also been addressed by the
functional programming community.  This includes work in
semantics-directed compilation as well as more general work by Alan
Mycroft (in his dissertation), David Schmidt (see a recent TOPLAS
paper about detecting "singlethreaded stores") and me (see POPL 85,
Lisp and FP 86).

The nice thing about doing all this in the functional programming
paradigm is that the implementation of an interpreter for a language
looks VERY MUCH (if not identical) to the formal semantics of the
language.  At Yale we have been experimenting a bit with such "truly
direct" semantics-directed compilation/interpretation with very
encouraging results.  Thus, assuming one believes in denotational
semantics (and I realize that some people don't...), then the answer
to Ken Kahn's question:

  A more interesting question I think is whether one language
  can EASILY and NATURALLY implement another.
would have to be in the affirmative.

    -Paul Hudak