Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!ncar!noao!arizona!gudeman
From: gudeman@cs.arizona.edu (David Gudeman)
Newsgroups: comp.lang.misc
Subject: Re: The Universal Language
Message-ID: <24384@megaron.cs.arizona.edu>
Date: 20 Aug 90 18:59:02 GMT
Organization: U of Arizona CS Dept, Tucson
Lines: 43

In article  <1990Aug20.143429.7659@ux1.cso.uiuc.edu> morrison@thucydides.cs.uiuc.edu (Vance Morrison) writes:
>>>In article <24281@megaron.cs.arizona.edu> gudeman@cs.arizona.edu (David Gudeman) writes:
>>..any ML program can be
>>translated into Smalltalk with a simple syntactic transformation.
                                   ^^^^^^
>>Furthermore, it is possible to select a subset of Smalltalk and
>>impute an ML-like semantics to that subset
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>...  The reverse is not possible.
>      ^^^^^^^^^^^^^^^^^^^^^^^^^^^

>I have to differ with you there.  Whenever you write semantics of a
>language what you are doing is specifying a SYNTATIC transformation
>from the source langauge to the semantic language.  Thus if I write
>the sematics of smalltalk in ML (which certanly is possible), I have
>just written a description that can be used to convert Smalltalk into
>ML.

The semantic description you are talking about is far from simple, and
has to specify every production in the grammer.  The syntactic change
from ML to Smalltalk, however can be specified as a general
tranformation.  Also, there is no subset of ML that corresponds to
Smalltalk.

All of my comments have been informal (they _can_ be formalized), but
the intuition can be given fairly clearly without talking about
homomorphisms and functors:  To an ML expression

  fun(arg1, arglist)

there corresponds a Smalltalk expression

  arg1 fun: arglist

where there are direct correspondences between the various parts of
the expression, and the Smalltalk expressions have no side-effects.
However, any side-effecting operation in Smalltalk has no
corresponding operation in ML.
-- 
					David Gudeman
Department of Computer Science
The University of Arizona        gudeman@cs.arizona.edu
Tucson, AZ 85721                 noao!arizona!gudeman