FP version of the animal guessing game, http://irclog.perlgeek.de/perl6/2014-12-13#i_9800695

fp-animal.p6

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

my &ask = decision("Does it swim", animal("fish"), animal("bird"));

while say("") && is-prompt-yes "Are you thinking of an animal? " {
    ask;
}

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

sub decision($q, $yes, $no) {
    -> {
        if is-prompt-yes("$q? ") {
            $yes()();
        }
        else {
            $no()();
        }
    }
}

sub animal($guess) {
    my $node = {
        if is-prompt-yes("Is it a $guess? ") {
            say "Why not try another animal?";
        }
        else {
            my $actual = prompt "The animal you were thinking of was a? ";
            say "Please type a question that would distinguish a $actual from a $guess";
            my $q = (prompt "? ").trim.subst(/\?$/, "");
            if is-prompt-yes "For a $actual the answer would be? " {
                $node = decision($q, animal($actual), animal($guess));
            }
            else {
                $node = decision($q, animal($guess), animal($actual));
            }
        }
    }

    return { $node };
}