#!/usr/bin/perl -w
use strict;

use Algorithm::Loops qw( NestedLoops );

my $permlist= [ 'a' .. shift(@ARGV)||'c' ];
my $max= $#$permlist;
my $card= shift(@ARGV) || 1;
my $iter= NestedLoops(
    [
        [ 0 .. $max+1-2*$card ],
        map( {
            my $left= $card - $_;
            sub { [ $_+1 .. $max+1-2*$left ] },
        } 1 .. $card-1 ),
        (
            sub {
                my %used;  @used{@_}= (1) x @_;
                [ grep !$used{$_}, $_[-$card]+1 .. $max ];
            },
        ) x $card,
    ],
);
## my @data;
my @idx;
while(  @idx= $iter->()  ) {
    my @group= map {
        [ @{$permlist}[ @idx[$_,$_+$card] ] ]
    } 0 .. $card-1;
    printf "( %s )\n", join ", ", map sprintf("(%s,%s)",@$_), @group;
    ## push @data, \@group;
}