sub charlist2alphabet {
    my %results;
    for my $index ( 0 .. (@_ - 1) ) {
        $results{ $_[ $index ] } = $index;
    }
    \%results;
}

my $alphabet = charlist2alphabet( @charlist );

##</code><code>##

my $alphabet = { map { ( $charlist[ $_ ] => $_ ) } ( 0 .. @charlist - 1 );