Re: How to return a list using recursion?

[Anonymous Monk]

Well, this isn't something you should use recursion for

#!/usr/bin/perl --
use strict; use warnings;
use Data::Dump;
use List::AllUtils qw' natatime ';
my @x = ('a' .. 'z');
my $it = natatime 5, @x;
my @yo;
while (my @vals = $it->())
{
    push @yo, "@vals,\n";
}
chomp $yo[-1];
chop  $yo[-1];
dd \@yo;
__END__
[
  "a b c d e,\n",
  "f g h i j,\n",
  "k l m n o,\n",
  "p q r s t,\n",
  "u v w x y,\n",
  "z",
]

[Athanasius]

this isn't something you should use recursion for

s/should/need to/

You also don’t need a module. Here is a solution using a stateful subroutine as an iterator:

#! perl
use strict;
use warnings;

my @list = ('a' .. 'z');
my $size = 5;

_array_chunk_it($size, @list);

while (my @chunk = _array_chunk_it())
{
    print "Array chunk of $size =\n", join("\n", @chunk), "\n\n";
}

{
    my ($array, $count);

    sub _array_chunk_it
    {
        my @chunk;

        if (@_)
        {
            $count = shift;
            $array = [ @_ ];
        }
        else
        {
            for (1 .. $count)
            {
                push(@chunk, shift @$array) if @$array;
            }
        }

        return @chunk;
    }
}

(With newer versions of Perl, this can be rewritten using state.)

TMTOWTDI :-)

Update: ++Anonymous Monk for the superior version using a closure, below.

[Anonymous Monk]

With older versions of Perl, it can be rewritten as a proper iterator :-)

use strict;
use warnings;

my @list = ('a' .. 'z');
my $size = 5;

my $chunker = _array_chunk_it($size, @list);

while (my @chunk = $chunker->())
{
  print "Array chunk of $size =\n", join("\n", @chunk), "\n\n";
}

sub _array_chunk_it {
  my ($count, @array) = @_;

  return sub {
    my @chunk;

    for (1 .. $count) {
      push(@chunk, shift @array) if @array;
    } 

    return @chunk;

  } 
}

(Using a closure we can actually call _array_chunk_it multiple times, in an overlapping manner. Have multiple iterators running simultaneously. Plus it looks quite a bit nicer.)

[Anonymous Monk]

this isn't something you should use recursion for

s/should/need to/

:) I meant should not, esp since there is nothing particularly recursive about it (you have to squint to make it recursive)

You also don’t need a module.

Sure I do :) otherwise I'm writing the the idiomatic perl solution

It was real hard to come up with

#!/usr/bin/perl --
use strict; use warnings;
my @x = ('a' .. 'z');
print yup( 5, @x ),"\n--\n";
print yup( 3, @x ),"\n";
sub yup {
    my( $n, @x ) = @_;
    my @yo;
    for( my $ix = 0; $ix < @x; $ix += $n )
    {
        my $high = $n - 1 + $ix ;
        $high > $#x and $high = $#x ;
        push @yo, join ' ', @x[ $ix .. $high ];
    }
    return join ",\n", @yo;
}
__END__
a b c d e,
f g h i j,
k l m n o,
p q r s t,
u v w x y,
z
--
a b c,
d e f,
g h i,
j k l,
m n o,
p q r,
s t u,
v w x,
y z