#! perl -slw
use strict;

sub nFor(&@) {
    my $code = shift;
    die "First argument must be a code ref" unless ref( $code ) eq 'CODE';
    my @limits = @_;

    my @indices = ( 0 ) x @limits;

    for( my $i = $#limits; $i >= 0; ) {
        $i = $#limits;
        $code->( @indices ), ++$indices[ $i ]
            while $indices[ $i ] < $limits[ $i ];
        $i = $#limits;
        $indices[ $i ] = 0, ++$indices[ --$i ]
            while $i >= 0 and $indices[ $i ] == $limits[ $i ];
    }
}

my @digits = 1 .. 3;

nFor {
    print join '', @digits[ @_ ];
} ( 3 ) x 4;