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From: pop@cs.umass.edu
Newsgroups: comp.lang.functional
Subject: Is Lisp in class X?
Message-ID: <14810@dime.cs.umass.edu>
Date: 25 May 90 17:15:00 GMT
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Re. article. <21581@megaron.cs.arizona.edu>, by David Gudeman.

I would say that most Lisps fall short of being in X because they do not
provide a proper treatment of function variables i.e.  you cannot say
(F X1 .... XN)  where  F is a variable - you have to do some funny
circumlocution which I don't remember. The binding of functions to function
names in LISP is of a different nature from variable bindings.

Scheme, somewhat tardily, provides a LISP dialect that gets it right. Oddly,
one of the reasons that Edinburgh got it right earlier (POP-2 -> Hope -> ML)
is that we had available a machine, the Eliot 4100 series, with an
instruction code designed by C.A.R.Hoare (et.al) c.1965. Hoare is not usually
thought of in that sort of role... I believe that he had Algol 60 in mind:
I do not think it was a very good Algol machine, since it was short of 
registers that could be used to implement a display, but the machine 
easily supported compilation of functional languages with little static 
typing, since it provided stacking instructions, an INDIRECT subroutine call,
and user-definable extracodes. In particular, the indirect subroutine call,
which was an unusual feature, made it natural to implement all function 
identifiers as variables. It also made it easy to do incremental compilation, 
with the function as the minimum unit of recompilation, and to write tracing 
procedures in the user language.


Robin Popplestone.