This is a pretty straight-forward use of Algorithm::Loops's NestedLoops():

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

use Algorithm::Loops qw( NestedLoops );

sub genIter
{
    my( $len, $base )= @_;
    return scalar NestedLoops(
        [ ( [ 0 .. ($base-1) ] ) x $len ],
        { OnlyWhen => 1 },
    );
}

my( $len, $base )= ( @ARGV, 4, 3 );
my $iter= genIter( $len, $base );
my @list;
while( @list= $iter->() ) {
    print @list, $/;
}
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