Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!nrl-cmf!mailrus!tut.cis.ohio-state.edu!bloom-beacon!athena.mit.edu!peter
From: peter@athena.mit.edu (Peter J Desnoyers)
Newsgroups: comp.lang.misc
Subject: Re: From Modula to Oberon
Message-ID: <3864@bloom-beacon.MIT.EDU>
Date: 18 Mar 88 05:20:40 GMT
References: <2827@enea.se> <1557@pasteur.Berkeley.Edu> <3764@bloom-beacon.MIT.EDU> <1130@PT.CS.CMU.EDU>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: peter@athena.mit.edu (Peter J Desnoyers)
Organization: Massachusetts Institute of Technology
Lines: 30
Keywords: iteration,

In article <1130@PT.CS.CMU.EDU> edw@IUS1.CS.CMU.EDU (Eddie Wyatt) writes:
>		***This is not a flame against the author.***
>   When will people learn, data abstraction is not a programming
>language or type of programming language, it is a programming
>methodology.
>  In particular if you want generalized iteration say in C, its
>a simple matter of defining an iteration function for that ...
>
>Eddie Wyatt 				e-mail: edw@ius1.cs.cmu.edu

Data abstraction is __assisted__ by the proper choice of programming
language. Note that the `for' construct in Pascal is not powerful 
enough to build such a general-purpose iterator - you would have
to do it with the more general `while' construct. Similarly, C does
not provide direct language support for co-routines, and constructing
an iterator that yields members of a recursive structure requires 
constructing an explicit static stack. (Similar to expressing a recursive
routine in a non-recursive Basic)

Try writing an iteration function in C for a binary tree. That may be 
data abstraction, but when you get done with it, it's going to look 
ugly because __C is not powerful enough to express general iterators
cleanly__.

I hope that I did not flame too much - it's late at night, and I wanted
to clarify my previous comments.


					Peter Desnoyers
					peter@athena.mit.edu