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From: alfh@byleist.ifi.uio.no (Alf-Ivar Holm)
Newsgroups: comp.lang.beta
Subject: Pattern variables
Followup-To: comp.lang.beta
Date: 06 Feb 1995 17:48:11 GMT
Organization: Dept. of Informatics, University of Oslo, Norway
Lines: 52
Message-ID: <ALFH.95Feb6184811@byleist.ifi.uio.no>
NNTP-Posting-Host: byleist.ifi.uio.no
CC: 

I have seen (a version of) the following program as an example of
using pattern variables in BETA:  
      
   ORIGIN '~beta/basiclib/current/betaenv';
   --- PROGRAM : descriptor ---
   (#
      intFunc: (# x,y: @integer enter x do inner exit y #);
   
      comp:
	(# f,g: ##intFunc; h: intFunc(# do x -> f -> g -> y #)
	enter (f##, g##)
	exit h##
	#);

      a: intFunc(# do x+x -> y #);
      b: intFunc(# do x*x -> y #);
      ab: ##intFunc;
      in: @integer;
   do
      (a##, b##) -> &comp -> ab##;
      'In: ' -> putText; getInt -> in;
      'Out: ' -> putText; in -> ab -> putInt; newline;
   #)
   
As far as I can see, the program below is doing the same, but
now with objects and dynamic references instead of pattern variables:
    
    ORIGIN '~beta/basiclib/current/betaenv';
    --- PROGRAM : descriptor ---
    (#
       intFunc: (# x,y: @integer enter x do inner exit y #);
    
       comp:
	 (# f,g: ^intFunc; h: intFunc(# do x -> f -> g -> y #)
	 enter (f[], g[])
	 exit &h[]
	 #);

       a: intFunc(# do x+x -> y #);
       b: intFunc(# do x*x -> y #);
       ab: ^intFunc;
       in: @integer;
    do
       (&a[], &b[]) -> &comp -> ab[];
       'In: ' -> putText; getInt -> in;
       'Out: ' -> putText; in -> ab -> putInt; newline;
    #)

Can someone please enlighten me on why pattern variables is the
thing to use in this context?

	Affi