I had to untangle it from it's dependancies with the object it is a method of, but this produces the sequence as show (prior to scrunching and formatting):

#! perl -slw
use strict;

sub gen {
    my( $len, $depth ) = @_;
    return () unless $len;
    return map {
        my $pre = $_;
        ( $pre, map{ $pre . $_ } gen( $len -1, $depth )  );    
    } 0 .. $depth - 1;
}

print for gen( 4, 3 );
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