use strict;
use warnings;

use 5.010;

sub groupsOf (&$@);

my @list = ( q{a} .. q{z} );

say for groupsOf { qq{@_,} } 5, @list;
say for groupsOf { qq{@_,} } 7, @list;

sub groupsOf (&$@)
{
    my $rcToRun  = shift;
    my $groupsOf = shift;

    my $rcDoIt;
    $rcDoIt = sub
       {
           $rcToRun->(
              map shift, 1 .. ( @_ < $groupsOf ? @_ : $groupsOf )
              ),
           @_ ? &$rcDoIt : ();
       };

    &$rcDoIt;
}

##</code><code>##

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,