Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!rochester!cornell!uw-beaver!apollo!mrst!sdti!turner
From: turner@sdti.SDTI.COM (Prescott K. Turner)
Newsgroups: comp.lang.misc
Subject: Re: first class functions (opps)
Summary: Equality is special.
Message-ID: <453@sdti.SDTI.COM>
Date: 10 May 89 02:40:00 GMT
References: <10253@orstcs.CS.ORST.EDU> <2400023@otter.hpl.hp.com> <451@sdti.SDTI.COM> <13638@watdragon.waterloo.edu>
Reply-To: turner@sdti.UUCP (0006-Prescott K. Turner, Jr.)
Organization: Software Development Technologies, Sudbury MA
Lines: 25


In article <13638@watdragon.waterloo.edu> akwright@watdragon.waterloo.edu (Andrew K. Wright) writes:
> Why?  What is so special about the equality operation over any
> other operation that it should take part in defining "first-class" functions?
> What about assignment?  Multiplication?  Addition?  Composition?
> 
> A language has first-class functions if any function can be passed
> as a parameter or returned as a result.  If the language provides
> an equality operation for functions, or an assignment operation,
> this is an independent issue.

I can't argue with this if it's the what most students of computer languages
understand by "first-class data type".  However, I believe it's possible
to state what's "so special" about assignment and equality.  Equality
of functions is well-defined in the mathematical domain used to specify
the semantics of the language at hand.  Assignment has a straightforward
meaning.  In both cases isn't it necessary to add a restriction to the
definition of a clean language in order to omit these operators?

Am I being naive?
-----
Prescott K. Turner, Jr.
Software Development Technologies, Inc.
P.O. Box 366, Sudbury, MA 01776 USA         (508) 443-5779
UUCP: ...{harvard,mit-eddie}!sdti!turner    Internet: turner@sdti.sdti.com