Animal guessing game, http://irclog.perlgeek.de/perl6/2014-12-13#i_9800695

animal.p6

class Guess {
    has Str $.question;
    has Guess $.yes;
    has Guess $.no;
    has Str $.animal;
    method is-a-question { ?$.question }
    method insert-question(
        :$!question,
        :$!yes = Guess.new(:$.animal),
        :$!no = Guess.new(:$.animal)) {
    }
    method Str { $.animal }
}

my $root = Guess.new(
    :question("Does it swim"),
    :yes(Guess.new(:animal<fish>)),
    :no(Guess.new(:animal<bird>)),
);

sub quit {
    multi animals($q where *.is-a-question) { animals($q.yes), animals($q.no) }
    multi animals($q) { $q.animal }
    say "";
    say "I now know these animals:";
    say "    $_" for animals($root);
    exit;
}

sub is-prompt-yes($question) {
    my $answer = prompt $question;
    quit() if !defined $answer;
    return so $answer.lc eq "y" | "yes";
}

say "Play 'Guess the animal'";
say "Think of an animal and the computer will try to guess it.";

while say("") && is-prompt-yes "Are you thinking of an animal? " {
    my $guess = $root;
    while $guess.is-a-question {
        if is-prompt-yes $guess.question ~ "? " {
            $guess.=yes;
        }
        else {
            $guess.=no;
        }
    }
    if is-prompt-yes "Is it a $guess? " {
        say "Why not try another animal?";
        next;
    }
    my $animal = prompt "The animal you were thinking of was a? ");
    my $actual = Guess.new(:$animal);
    say "Please type a question that would distinguish a $actual from a $guess";
    my $question = (prompt "? ").trim.subst(/'?'$/, '');
    if is-prompt-yes "For a $actual the answer would be? " {
        $guess.insert-question(:$question, :yes($actual));
    }
    else {
        $guess.insert-question(:$question, :no($actual));
    }
}
quit;