Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!usc!jarthur!sburke
From: sburke@jarthur.Claremont.EDU (Scott Burke)
Newsgroups: comp.sys.handhelds
Subject: Re: HP48:Errorhandling help,strange feature and a little problem
Keywords: HP48 Error
Message-ID: <11807@jarthur.Claremont.EDU>
Date: 19 Apr 91 06:18:20 GMT
References: <1548@tau.sm.luth.se>
Distribution: comp
Organization: Harvey Mudd College, Claremont, CA 91711
Lines: 55


Let me generalize this problem a little bit, and further ask for a solution:

I write a user-defined function in user-RPL, like this one:

PLUS
\<<
   \-> a b
   \<<
      a b +
   \>>
\>>

If there are too few arguments, then I get an error message like:

\-> Error:
Too Few Arguments

Now on to a more complicated example:

DIVIDE
\<<
   \-> a b
   \<<
      IFERR
         a b /
      THEN
         -55 FC? { a b } IFT       @ restore LastArgs if -55 clear, to
                                   @ mimic the HP-48SX behavior
         "DIVIDE Error:\010"       @ \010 is a newline
         ERRM + DOERR              @ repeat the error, but with "DIVIDE..."
      END
   \>>
\>>

This routine (and the obvious extensions to it, which involve type-checking
the two variables 'a' and 'b') will mimic the built-in '/' operator, except
for one situation:  Too Few Arguments.  Since I want a user-defined function,
I _must_ immediately do the "\-> a b" command to get the arguments, without
first checking that at least two things are on the stack.  If I could check
that two things were on the stack, I could provide the desired error:

DIVIDE Error:
Too Few Arguments

As it is, I must make do with the "\-> Error:\010Too Few Arguments" version.

It's a minor quibble, but I am curious as to how to trigger or control the
built-in error handler.  I'm not looking for machine-language solutions, but
perhaps a simple SYSEVAL or two that I can plop into a user-language routine.

Any ideas?

Scott
sburke@jarthur.claremont.edu