Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!spool.mu.edu!snorkelwacker.mit.edu!stanford.edu!agate!usenet.ins.cwru.edu!po.CWRU.Edu!rkb
From: rkb@po.CWRU.Edu (Robert K. Brunner)
Newsgroups: comp.sys.handhelds
Subject: HP-48 programming problem
Message-ID: <1991Apr9.021224.27070@usenet.ins.cwru.edu>
Date: 9 Apr 91 02:12:24 GMT
Sender: news@usenet.ins.cwru.edu
Reply-To: rkb@po.CWRU.Edu (Robert K. Brunner)
Organization: Case Western Reserve University, Cleveland, OH (USA)
Lines: 27
Nntp-Posting-Host: cwns10.ins.cwru.edu


I had a problem debugging a program today, and I was wondering if anyone
had encountered the same problem before.  The problem isn't a bug, but
it is annoying behavior.

Suppose you have the following variables:

P1: \<< \-> a \<< 'a' INC \>> \>>
INC: \<< \-> a \<< a INCR DROP \>> \>>

Executing 5 P1 gives INCR Error: Bad Argument Type.
If you change the local variable in either of the programs to something 
different, you get 6, as you would expect.  Apparently, INC thinks
that the 'a' on the stack refers to the innermost local variable,
rather than the one belonging to P1.  If this behavior is documented
in the manuals, I haven't seen it.  

By the way, I worked around the problem by using pass-by-value in
the real program.  Unfortunately, the reason I use a sub-program
is that I need the routine in three places, so I've got three
extra " 'a' STO " 's, one after each call of the routine.  I may
change the local variable in the routine, but it bothers me that
subroutine calls are not transparent.  Suppose someone writes a
library that uses a local variable which I unwittingly use elsewhere.

Robert