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From: joel@decwrl.UUCP (Joel McCormack)
Newsgroups: net.lang,net.lang.mod2
Subject: Re: Modula-2 an insuggicient language
Message-ID: <398@decwrl.UUCP>
Date: Wed, 30-Jan-85 18:58:34 EST
Article-I.D.: decwrl.398
Posted: Wed Jan 30 18:58:34 1985
Date-Received: Fri, 1-Feb-85 21:24:10 EST
Organization: DEC Western Software Lab, Los Altos, CA
Lines: 47


    Modula-2 IS a good language for hacking, in fact, it was the combination
of type-checking and low-level access that first got me interested in the
language.

    David Sher's "problem" with dynamic arrarys is actually pretty easy.

    TYPE DynamicArray = POINTER TO ARRAY [0..0] (* [0..MaxInt] is also good *)
			   OF CARDINAL (* or whatever *);

         Image = RECORD
		    numberColumns: CARDINAL;
		    numberRows   : CARDINAL;
		    image	 : DynamicArray;
		    END;

... assume you have just filled in numberColumns and numberRows...

WITH Image DO
   ALLOCATE (image, numberColumns*numberRows*TSIZE(CARDINAL));
   END;

...accessing row, column, assuming 0-based...
(* turn off range-checking if used [0..0] *)
WITH Image DO
   image^[row*numberColumns + column] := ...
   END;


    Now, is that really significantly different from C?  I would prefer to
have support for dynamic arrays directly in the language, so that you
wouldn't have to do your own array subscript calculations, and you could get
range-checking as part of the normal indexing operation.  But Modula-2 is
certainly USABLE for this kind of thing.

    A real-life example is a Modula-2 program called StatPak by Richard
Sincovec and Richard Wiener.  This programs implements virtual arrays that
can exist on disk, or in memory, and made use of the technique above.  They
also claimed that since they had modules to help get the organization of the
program down, and type-checking to keep them from spending the rest of their
lives debugging, they were able to include substantially more goodies running
at a higher speed than the other statistical packages for micros.

-- 
- Joel McCormack {ihnp4 decvax ucbvax allegra sequent utcsrgv}!decwrl!joel
		 joel@decwrl.arpa