User defined function in while loop

kgherman has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks, I'm trying to write a while loop and I'm running into some problems with the condition that I need to put in the loop. I would like to know if I can put as a condition a user defined function that has an outcome of TRUE or FALSE.

I'm not very familiar with how to write such type of functions so before I venture into this I would like to know whether it's doable to begin with.

Comment on User defined function in while loop

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Re: User defined function in while loop by toolic (Bishop) on Jun 19, 2015 at 18:43 UTC
Yes. This considers 1 as TRUE and 0 as FALSE: `use warnings; use strict; my $i = 0; while (foo($i)) { print "i = $i\n"; $i++; } sub foo { my $x = shift; return ($x < 5) ? 1 : 0; } __END__ i = 0 i = 1 i = 2 i = 3 i = 4` [download]	[reply] [d/l]
Re: User defined function in while loop by ikegami (Patriarch) on Jun 19, 2015 at 18:41 UTC
Yes, you must provide an expression that returns a true or false value, and sub calls are expressions. `while (more(...)) { ... }` [download] `while (!done(...)) { ... }` [download] `while (my $item = get(...)) { ... }` [download]	[reply] [d/l] [select]
Re: User defined function in while loop by Laurent_R (Canon) on Jun 19, 2015 at 20:15 UTC
Sure you can. As exemplified in this simple command-line (one-liner) script; `$ perl -E 'my $count = 5; say $count while decr($count); sub decr {-- +$_[0];}' 4 3 2 1` [download] Note that, in this case, $_[0] is an alias for $count, so that decrementing $_[0] does decrement $count. Not necessarily a best practice in general, but OK IMHO for a one-liner. Or a variation of the same not using aliases: `$ perl -E 'my $count = 5; say $count while $count = decr($count); sub + decr {return -1 + shift;}' 4 3 2 1` [download]	[reply] [d/l] [select]