# you can use print for debugging purposes, e.g.
# print "this is a debug message\n";
use Data::Dumper;

sub solution {
    my ($L)=@_;
    print Dumper $L;
    # write your code in Perl 5.14
}

##</code><code>##

Running solution...

Compilation successful.

Example test:   [1, 1, 1, 1]
Output (stderr):
WARNING: producing output may seriously slow down your code!
Output: