Path: utzoo!attcan!uunet!samsung!uakari.primate.wisc.edu!uflorida!haven!uvaarpa!mmdf
From: alfie%cs.warwick.ac.uk@nsfnet-relay.ac.uk (Nick Holloway)
Newsgroups: comp.lang.perl
Subject: $1, $2 not being set - array/scalar context confusion?
Message-ID: <1990Mar21.165957.9520@uvaarpa.Virginia.EDU>
Date: 21 Mar 90 16:59:57 GMT
Sender: mmdf@uvaarpa.Virginia.EDU (Uvaarpa Mail System)
Reply-To: alfie%cs.warwick.ac.uk@nsfnet-relay.ac.uk
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There was recently a thread about a problem with $1 not being set when
a subroutine was called in an array context. I think I understood what
was happening. I am having a problem that is similar in some ways.

What I would like, is either confirmation that I have discovered a bug
in perl (and that it will be fixed - Larry?), or that I have done
something silly, and an explanation of why, and how to avoid it.

I have a problematic routine that is supposed to do range expansion, so
"1,3-5" becomes "(1,3,4,5)". It splits at the delimiter (either "," or
" "), and then looks for terms of the form "\d+" or "\d+-\d". The
latter causes the problem, since if called in an array context (which is
pretty useful if you want to use the array of values!), the pattern
"^(\d+)-(\d+)$" fails to set $1 and $2.

I am willing to be convinced that this is some problem to do with
array/scalar context, but my doubts stem from:

    a) I have an explicit statement to return the array at the end 
       (This was a solution for previous posters problem). From what I
       understood from before - the context the routine was called in
       was affecting the evaluation of "if". Does this apply here?  

    b) If the routine is called in an scalar context, with a pattern
       that contains a "\d+-\d+" term, the routine works as expected in
       later calls.

[I currently have a call to &expand("0-0") in the perl script to start
 it working, commented with "BUG workaround", and my bug logo (see
 .sig) -- it would be nice to be able to remove it]

Following my signature is the code that causes me grief. Also there is
the result of running it through perl, patchlevel 15. (same as 6 & 8 -
I didn't ever have 12).

	Here's hoping that someone can help me,
				Alfie
--
Nick Holloway |  `O O'  | alfie@cs.warwick.ac.uk, alfie@warwick.UUCP,
[aka `Alfie'] | // ^ \\ | ..!uunet!mcsun!ukc!warwick!alfie
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
	sub expand {
	    local ( $arg ) = shift;
	    local ( @nums, $i );

	    print "debug: input = $arg\n";
	    $arg =~ s/\s+([-,])\s+/\1/g;
	    $arg =~ s/\s+/,/g;
	    split ( /,/, $arg );
	    for ( @_ ) {
		if ( /^\d+$/ ) { 
		    print "debug: term = $_\n";
		    push ( @nums, $_ ); 
		    next;
		} elsif ( /^(\d+)-(\d+)$/ ) {
		    print "debug: term = $_ : from ", $1, " to ", $2, "\n";
		    for ( $i = $1; $i <= $2; $i++ ) {
			push ( @nums, $i );
		    }
		    next;
		} else {
		    print "debug: bad term - abandon ship!\n";
		    @nums = ();
		    last;
		}
	    }
	    print "debug: output = @nums\n\n";
	    @nums;
	}

	@a = &expand ( "0-2" );		# fails to expand
	$a = &expand ( "1" );		# doesn't trigger correct operation
	@a = &expand ( "1-3" );		# fails to expand
	$a = &expand ( "2-4" );		# This call starts it working
	@a = &expand ( "3-5" );		# works correctly
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
	debug: input = 0-2
	debug: term = 0-2 : from  to 
	debug: output = 

	debug: input = 1
	debug: term = 1
	debug: output = 1

	debug: input = 1-3
	debug: term = 1-3 : from  to 
	debug: output = 

	debug: input = 2-4
	debug: term = 2-4 : from 2 to 4
	debug: output = 2 3 4

	debug: input = 3-5
	debug: term = 3-5 : from 3 to 5
	debug: output = 3 4 5