文字列の長さはchars
Perl6では、文字列の長さはlengthではなくcharsで得られる。
my $strlen = $str.chars;
length: This word is banned in Perl 6. You must specify units.
http://perlcabal.org/syn/S32/Str.html
chars: Returns the number of characters in the string in the current (lexically scoped) idea of what a normal character is, usually graphemes.