Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!cornell!rochester!PT.CS.CMU.EDU!IUS1.CS.CMU.EDU!edw
From: edw@IUS1.CS.CMU.EDU (Eddie Wyatt)
Newsgroups: comp.lang.misc
Subject: Re: From Modula to Oberon
Message-ID: <1130@PT.CS.CMU.EDU>
Date: 15 Mar 88 19:35:51 GMT
References: <2827@enea.se> <1557@pasteur.Berkeley.Edu> <3764@bloom-beacon.MIT.EDU>
Sender: netnews@PT.CS.CMU.EDU
Organization: Carnegie-Mellon University, CS/RI
Lines: 32

> 
> I wish they had put iterators in Ada. C provides a general linear
> iterator, but in CLU you can iterate through a tree or anything else.
> After all, the idea of iterating is so that you can separate the
> structure of bunch of data from the logic of:
> 
> for each foo in bar
>   do something
> end
> 

		***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 particular
data type.  Provide it a reset flag to start iteration,
either a static var or extra field in the data type representing
the current object and some termination object.

    for (object = iter_func(data_struct,START); 
	 object != TERMINATOR;
	 object = iter_func(data_struct,NEXT)) {....}

I do this for my generic hash tables in C when I need to dump the
them in linear format.
-- 

Eddie Wyatt 				e-mail: edw@ius1.cs.cmu.edu