Path: utzoo!utgpu!watserv1!watmath!iuvax!mailrus!ncar!boulder!ruede
From: ruede@boulder.Colorado.EDU (Ulrich Ruede)
Newsgroups: comp.lang.c
Subject: Re: Personal dialects and C++ overloading
Summary: Macros for customizing C
Message-ID: <16477@boulder.Colorado.EDU>
Date: 2 Feb 90 02:36:37 GMT
References: <5940014@hpcupt1.HP.COM> <Jan.24.10.40.15.1990.15842@police.rutgers.edu> <33889@ucbvax.BERKELEY.EDU> <1922@gmdzi.UUCP> < <1990Jan29.210357.366@eng.umd.edu> <90029.194640JI8@PSUVM.BITNET> <4152@helios.TAMU.EDU> <33478@news.Think.COM> <4156@helios.TAMU.EDU>
Sender: news@boulder.Colorado.EDU
Reply-To: ruede@boulder.Colorado.EDU (Ulrich Ruede)
Organization: University of Colorado, Boulder
Lines: 72

In article <4156@helios.TAMU.EDU> john@stat.tamu.edu (John S. Price) writes:
>
>#define FORNEXT(x,y,x)  for (x=y;x<z;++x)
>
>...
>FORNEXT(x,0,10);
>
>That is not standard C, and I feel that using this type of macro is
>bad coding style.  
>

Well, knowing that the following program has to do with a graph (with
attributed nodes and edges) would you prefer to see an initialization
like

	FOR_ALL_NODES_OF(a_mesh, this_node)
		FOR_ALL_EDGES_OF(this_node, this_edge)
			this_edge->component= 0;
		END_ALL_EDGES
	END_ALL_NODES

or rather

	{	
		Node_Ptr this_node;
		for(this_node= (a_mesh)->grd; (this_node) != NULL; (this_node)= (this_node)->next){
			{ register Edge_Ptr	this_edge= (this_node)->c,
			_end= (this_edge)+((this_node)->num_edges);
			for(; (this_edge)<_end; (this_edge)++){
				this_edge->component= 0;

			}
		}
	}
	}

This has been produced by cb on the expanded result.

The macros enable me to define the data structures and the access to
these structures together, as one module. If I don't use macros, the
information how to access all nodes of the graph is dispersed throughout
the program. Changing the basic structure then means to rewrite
everything. If I have the macros, I need to change just the macro definition.

I am using m4, so everyone who prefers the expanded result, can easily
get it with all symbolic constants still in symbolic form.

I also think that changing the syntax of a language is not a bad thing by
itself. If you write a function, you have also changed the syntax
of the language by introducing a new terminal symbol at the expression
level. In some sense all programming consists in changing the syntax
of a given base language, until you have a *specialized language* in which
you solve your problem with a single statement like
	work();
This view of programming may be more obvious users of languages like
Prolog or Forth.

I agree, that only because you dislike C syntax you shouldn't
do things like
	#define BEGIN {
(if you can't see the braces, get a better terminal (:-) or
	#define OR ||
just as you wouldn't introduce new names for printf and other standard
library functions. Writing your own subroutines, however, makes perfect
sense, just as I believe it makes sense to use macros as mine above.
It would still be better if these capabiltities were built into some language
(without sacrificing performance).

Ulrich Ruede

ruede@boulder.colorado.edu (until Friday)
ruede@infovax.informatik.tu-muenchen.dbp.de (next week)