Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!decwrl!ucbvax!bloom-beacon!THINK.COM!gls
From: gls@THINK.COM (Guy Steele)
Newsgroups: comp.lang.scheme
Subject: What is a Scheme?
Message-ID: <9008211445.AA02571@mozart.think.com>
Date: 21 Aug 90 14:45:45 GMT
References: <TED.90Aug20125352@kythera.nmsu.edu>
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 36


I would like to plead for a little flexibility and tolerance in
the question of "What is Scheme?".  Scheme has evolved quite a bit
over the last 15 years and it seems to me to be too rigid to
disqualify an implementation because it lacks a few string
functions or even because it lacks CALL/CC.  That may disqualify
it from being Scheme R^3.95 or whatever, but not, in my eyes, from
belonging to the Scheme family.  The original 1975 Scheme didn't
have any string functions, but surely it may still be regarded as
a Scheme at least to the extent that Lisp 1.5 is still regarded as
a Lisp.

Allow me to offer my opinion on what makes a Scheme:

	lambda calculus, which includes:
	  variables, lexically scoped
	  lambda expressions that evaluate to first-class closures
	  combinations (i.e., function calls) with the same evaluation
	    rule used for all positions (function and arguments)

	Lisp syntax, probably
	a standard representation for programs as data, probably
	  (typically as lists and symbols)

	a means of manipulating continuations, maybe
	  (best if they are first-class)
	a primitive side effect on variables or data, maybe

I regard all other data types, including numbers and strings,
as entirely inessential to Scheme-ness.  The same goes for
control structures (I'll just synthesize DELAY and FORCE
myself from closures and side effects).

So there is one opinion.  Let's hear some others.

--Guy