use Perl

• returning refs? (Score:1)

  by Eric Wilhelm (6389)

  Why not return []'s which get flattened into the output until undef is returned?

      my @rev = induce {@$_ ? pop @$_ : undef} [1..10];

  But maybe I'm missing something as to why the prototype is &$ instead of &@, or am just wanting a better example? I would think that unfold might be more like:

      my @flat = map({map({$_} @$_)} [1..10],[12..20]);

  or thereabouts - and the 'reverse' example does not clarify that for me.
  • Re: (Score:1)

    by Aristotle (5147)

    Why not return []’s which get flattened into the output until undef is returned?

    Because then there has to be an escape mechanism for the block to be able to return an actual [] that should be preserved in the output, and the block has to make sure to use it when appropriate.

    But maybe I’m missing something as to why the prototype is &$ instead of &@

    Because unfold (“induce”) takes a single value and inflates it to a list, as opposed to fold (reduce) which takes a list and def
    • Re:returning refs? (Score:1)

      by Eric Wilhelm (6389) on 2009.01.16 19:17 (#66903) Homepage Journal

      Why not return []’s which get flattened into the output until undef is returned?

      Because then there has to be an escape mechanism for the block to be able to return an actual [] that should be preserved in the output, and the block has to make sure to use it when appropriate.

      No, you would not reach inside the returned ref - only flatten it at the first level. It is either [] or undef, so [[]] would be a list of one reference.

      
    my @power = induce {
        my $r = $_ % 12
        $_ /= 12;
        return $r ? [$r] : undef;
    } 4711;


    my @chunk = induce {
      (length) ? [substr $_, 0, 3, ''] : undef
    } "foobarbaz";


      The return $condition ? [@stuff] : undef seems like it might be forming a pattern.

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