NAME

Loop::Util - loop helper keywords

SYNOPSIS

use Loop::Util;

my @array = qw(foo bar baz quux);

for my $item (@array) {

  iffirst {
    print "Items\n";
    print "-" x length($item), "\n";
  }
  
  print "$item\n";
  
  iflast {
    print "-" x length($item), "\n";
    print "Count: ", scalar(@array), "\n";
  }
}

DESCRIPTION

This module adds statement keywords:

• loop BLOCK, loop (EXPR) BLOCK

  loop introduces new loop forms.

  loop { ... }
  loop(3) { ... }
  loop(get_number()) { ... }

  loop also supports a single-statement form:

  loop process_input();
  loop(3) process_input();

  Parentheses are required around the loop count expression. If no count is given, the loop is infinite, but last can be used to jump out of the loop. (The next and redo keywords also work as expected.)

• iffirst [LABEL] BLOCK [else BLOCK]

  Runs BLOCK only on the first loop iteration; if an else block is present it runs for subsequent iterations.

  When LABEL is present, iffirst checks that labeled loop context instead of the innermost loop. This is useful in nested loops:

  OUTER: loop(2) {
    loop(3) {
      iffirst OUTER { say "hi" }
    }
  }

  iffirst works in loop{} loops, and also in for/foreach loops over arrays and lists. Calling iffirst in other loop kinds throws a runtime error.

• iflast [LABEL] BLOCK [else BLOCK]

  Runs BLOCK only on the last loop iteration; if an else block is present it runs for not-last iterations.

  When LABEL is present, iflast checks that labeled loop context instead of the innermost loop.

  iflast works in finite loop{} loops, and also in for/foreach loops over arrays and lists. Calling iflast in other loop kinds throws a runtime error.

• ifodd [LABEL] BLOCK [else BLOCK]

  Runs BLOCK for odd-numbered iterations (1st, 3rd, 5th...). If an else block is present, it runs on even-numbered iterations.

  Note that if you loop through an array, the first iteration (an odd iteration) has index number 0 (an even number).

  When LABEL is present, ifodd checks that labeled loop context instead of the innermost loop.

  ifodd works in loop{} loops, and also in for/foreach loops over arrays and lists. Calling ifodd in other loop kinds throws a runtime error.

• ifeven [LABEL] BLOCK [else BLOCK]

  Runs BLOCK for even-numbered iterations (2nd, 4th, 6th...). If an else block is present, it runs on odd-numbered iterations.

  Note that if you loop through an array, the first iteration (an odd iteration) has index number 0 (an even number).

  When LABEL is present, ifeven checks that labeled loop context instead of the innermost loop.

  ifeven works in loop{} loops, and also in for/foreach loops over arrays and lists. Calling ifeven in other loop kinds throws a runtime error.

• __IX__

  Psuedo-constant that returns the current zero-based index of the loop.

  It should work for loop{} loops as well as for/foreach loops over arrays or lists. In other contexts where no index can be determined, it returns undef.

BUGS

Please report any bugs to https://github.com/tobyink/p5-loop-util/issues.

SEE ALSO

Acme::Loopy, Syntax::Keyword::Loop.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2026 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.