jerbil@cit-vax.Caltech.Edu (Stainless Steel Gerbil [Joe Beckenbach]) (01/18/90)
Is there a way to force a subroutine to return a null array?
Or. rather, I would like to do this:
open( FILE, $file );
@array = do subrtn( $stuff, $n, $nonsense );
while ( $#array >= 0 ) {
# fiddle $stuff and $nonsense
# ...
} continue {
@array = do subrtn( $stuff, $n, $nonsense );
}
close( FILE );
I would be grateful if someone would present a way to do this, for the way
I'm trying to work things may be tripping a bug in my copy of perl, and I'm a
bit beyond my frustration point at the moment to try tracking down whether
it's a bug in perl or an error in my understanding of its behavior. [Most
likely the latter, but after about four hours one begins to wonder....]
Thanks ever so much.
Joe Beckenbach
--
Joe Beckenbach jerbil@csvax.caltech.edu VEGGIES FOREVER!
Toto, kansasoseum nun est cognito. -- Farleyhakanson@ogicse.ogc.edu (Marion Hakanson) (01/19/90)
In article <13395@cit-vax.Caltech.Edu> joe@cit-750.cs.caltech.edu (Joe Beckenbach) writes: > > Is there a way to force a subroutine to return a null array? Now that you mention it, I've been wondering about some odd behavior related to that for awhile. I have a workaround, and I forgot to track it down further. Here's the workaround: while ( (@a = do subr()) && @a ) { # fiddle with @a } Now I just tracked it down further. Here's a test program which demonstrates the problem (perl 3.0, pl6, anyway -- I didn't notice a patch in 7&8): ==========cut here=========== #!/usr/bin/perl sub nsub1 { (); } sub nsub2 { return (); } @nr1 = do nsub1(); print "nr1 has $#nr1 elements.\n"; @nr2 = do nsub2(); print "nr2 has $#nr2 elements.\n"; ==========cut here=========== Here's the output: nr1 has -1 elements. nr2 has 0 elements. It turns out that $nr2[0] is empty, which is why my "workaround" works. Definitely looks like a bug to me, though. Larry? -- Marion Hakanson Domain: hakanson@cse.ogi.edu UUCP : {hp-pcd,tektronix}!ogicse!hakanson
jerbil@cit-vax.Caltech.Edu (Stainless Steel Gerbil [Joe Beckenbach]) (01/19/90)
In my article <13395@cit-vax.Caltech.Edu> I write: > Is there a way to force a subroutine to return a null array? > [... more stuff ...] Amazing what a good night's sleep will do for a body. Found my problem (of course it was my error, Larry!) and discovered the do { } while construct, which simplified my script's logic to the point that I discovered my errors. Joe -- Joe Beckenbach jerbil@csvax.caltech.edu VEGGIES FOREVER! Toto, kansasoseum nun est cognito. -- Farley
jerbil@cit-vax.Caltech.Edu (Stainless Steel Gerbil [Joe Beckenbach]) (01/20/90)
In his article, Marion Hakanson <hakanson@ogicse.UUCP> produces a script that reflects the problem I was having. Bravo for locating the source of my frustration on little evidence! I've fetched a completely fresh copy for my machines and will try to cajole my friends to keep in sync with it. The copy that was causing the heartache seems to have been 3p4 at best, from what little I can find. Thanks again, all, for forgiving me my low signal:noise. Joe Beckenbach -- Joe Beckenbach jerbil@csvax.caltech.edu VEGGIES FOREVER! Toto, kansasoseum nun est cognito. -- Farley
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) (02/06/90)
In article <6712@ogicse.ogc.edu> hakanson@ogicse.UUCP (Marion Hakanson) writes: : In article <13395@cit-vax.Caltech.Edu> joe@cit-750.cs.caltech.edu (Joe Beckenbach) writes: : > : > Is there a way to force a subroutine to return a null array? : : Now I just tracked it down further. Here's a test program which : demonstrates the problem (perl 3.0, pl6, anyway -- I didn't notice : a patch in 7&8): : : ==========cut here=========== : #!/usr/bin/perl : : sub nsub1 : { : (); : } : : sub nsub2 : { : return (); : } : : : @nr1 = do nsub1(); : print "nr1 has $#nr1 elements.\n"; : : @nr2 = do nsub2(); : print "nr2 has $#nr2 elements.\n"; : ==========cut here=========== : : Here's the output: : : nr1 has -1 elements. : nr2 has 0 elements. : : It turns out that $nr2[0] is empty, which is why my "workaround" : works. Definitely looks like a bug to me, though. Larry? This turned out to be a syntactic problem. I had made return be a list operator so that you can say return 1,2,3; Unfortunately, like other list operators, if the next token was a left paren, that and the matching paren were taken to delimit the entire function. So return () transmogrified itself into (return); and there went the null array. This suggest several workarounds. You can say any of return (()); return ((),()); return +(); # !!! return @nullarray; return 1..0; The best solution, since return (123),456; makes no sense, is to exempt "return" from the parenthesis rule for other list operators, and have it ignore the parens. It then will do what is expected in almost every case. Larry