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Scheme Digest #9
- To: Scheme@MC.lcs.mit.edu
- Subject: Scheme Digest #9
- From: firstname.lastname@example.org
- Date: Wed ,16 Nov 88 10:28:18 EDT
- In-reply-to: Automatic Scheme Digestifier's message of 16 NOV 88 00:11:14 EST <8811160652.AA19419@theory.LCS.MIT.EDU>
> Mark VandeWettering writes:
> I think (and my thesis work is evolving into this kind of
> argument) that Y is overlooked for trivial reasons. Partial
> evaluation and smarter code generation could make an SK based
> compiler generate code which is equal in quality to that produced
> by supercombinator based compilation.
I thought that the reason for using supercombinators rather than S and K is
space. Ordinary \-calculus expressions can be translated into SK-combinatory
expressions, but the combinatory version is exponentially longer than the SK
term. Some sets of supercombinators give polynomial-length expansions; I
think some give linear expansions.
Now, code size isn't usually much of a problem, in that we don't
usually care whether a program is 50K or 250K. The difference between 50K
and 2^50K is significant. I don't know if the translation has a decent
expected case or not.
In any event, the SK compiler has a lot of work to do before it can match
even a fairly stupid supercombinator compiler, simply because it can be
forced to produce incredibly long code. My guess, and I gather the guess of
many people who actually work on this, is that SK would lose. I would be
very interested in some proof that this guess was wrong.
-- Bard Bloom