Perl 6 ExamplesBlackjack!
Author: David Whipp
In Blackjack! competitors must write a script that deals and plays a single hand of Blackjack (Twenty-One).
Event Scenario
For the final event in the Advanced Division you must write a script that can deal – and play – a single hand of Blackjack (also known as Twenty-One). For the purposes of this event, we’ll be playing a simplified version of Blackjack, one that features the following rules:
No betting is involved. (Sorry; maybe next year.)
All aces are worth 11 points. And yes, we know: in standard Blackjack, aces can be worth either 1 point or 11 points. For Event 10, however, aces will only be worth 11 points. (We don’t want to make this event too complicated.)
Oh, OK: if you want to you can make aces worth 1 or 11. But you don’t have to do this unless you want to.
All face cards (Kings, Queens, Jacks) are worth 10 points.
All other cards are equal to their face value: the three of spades is worth 3 points, the 7 of diamonds is worth 7 points, etc.
Ties (pushes) go the dealer. Suppose, at the end of the hand, the player has 18 points and the dealer has 18 points. In that case, the dealer is declared the winner.
Your script should start by “shuffling” a standard deck of playing cards and then dealing two cards to the player and two more to the dealer. (Not sure what cards make up a ‘standard deck of playing cards?” Then click here for more information.) As in regular blackjack, the two cards to the player should be dealt “face up;” that is, both cards should be revealed:
Your cards: Seven of Spades Eight of Spades
By contrast, only one of the dealer’s cards should be revealed:
Dealer's cards: Ace of Hearts
Note. Notice that we specified the cards by name. Don’t just list card values, like this:
7 8
That will cause your script to fail. Be specific when it comes to listing cards.
Again, following standard Blackjack rules, the player should be given the option to stay (play the two cards he or she was dealt) or hit (be dealt another card). In other words:
Stay (s) or hit (h) ?
If the player chooses “hit,” then he or she should be dealt another card. If the sum total of the three cards is more than 21, then the player automatically loses:
Stay (s) or hit (h) ?h Seven of Spades Eight of Spades Seven of Diamonds Over 21. Sorry, you lose.
If the sum total is 20 or less, then the player is given another opportunity to hit or stay. (If the sum total is 21 the player wins.) As soon as the player chooses to stay, the dealer (the computer) checks to see if its point total exceeds that of the player. For example, suppose the player has the seven of spades and the eight of spades; that means that the player has 15 points. Now suppose that the dealer has the ace of hearts and the six of diamonds. That means that the dealer has 17 points (11 + 6), which also means that the dealer automatically wins.
Now, suppose the player has 16 points and the dealer has 13. In that case, the dealer must be dealt another card. Let’s examine some possibilities for that next card:
The dealer is dealt a two, giving the dealer 15 points. That’s less than the player’s 16, so the dealer must go again.
The dealer is dealt a nine, giving it 22 points. 22 is more than 21, so the dealer loses.
The dealer is dealt a three, giving both the dealer and the player 16. Because ties go to the dealer, the dealer automatically wins.
A complete hand might play out something like this:
Your cards: King of Hearts Seven of Hearts Dealer's cards: Nine of Hearts Stay (s) or hit (h)?s You have 17. Dealer's cards: Nine of Hearts Seven of Diamonds Dealers' cards: Nine of Hearts Seven of Diamonds Five of Diamonds The dealer has 21. Sorry, you lose.
See? That shouldn't be too terribly hard, especially not for anyone who made it through the first nine events.
Source code: event010-dwhipp.p6
use v6;
sub MAIN(Bool :$computer-player = False) {
my $player_is_human = not $computer-player;
my @values = (
ace => 1|11,
two => 2,
three => 3,
four => 4,
five => 5,
six => 6,
seven => 7,
eight => 8,
nine => 9,
ten => 10,
jack => 10,
queen => 10,
king => 10,
);
my @suites = < spades clubs diamonds hearts >;
my @deck = ( @values X @suites ).flat.map: {
my ($name, $value) = $^a.kv;
$name ~= " of $^b";
$name => $value
};
my @cards = $computer-player ?? default-cards() !! @deck.pick( @deck.elems );
my @dealer;
my @player;
@dealer.push( @cards.shift );
@player.push( @cards.shift );
@dealer.push( @cards.shift );
say "DEALER:";
say @dealer[0].key;
say "";
say "PLAYER:";
.key.say for @player;
my $player_value = [+] @player.map: { .value };
loop {
my $card = @cards.shift;
@player.push( $card );
say $card.key;
$player_value += $card.value;
say "current value is { $player_value.perl }";
if $player_value == 21 {
say "congratulations, you win!";
exit 0;
}
elsif $player_value < 21 {
say "hit (h) or stay (s)";
my $choice;
if ($player_is_human) {
loop {
$choice = lc $*IN.get;
last if $choice eq "h" | "s";
say "invalid entry: 'h' or 's'";
}
}
else {
$choice = $player_value < 16 ?? "hit" !! "stay";
}
say $choice;
last if $choice ~~ /s/;
}
else {
say "sorry, you bust!";
exit 0;
}
}
say "";
$player_value = max (4 .. 21).grep: { $_ == $player_value };
say "DEALER:";
.key.say for @dealer;
my $dealer_value = [+] @dealer.map: { .value };
loop {
say "dealer value: {$dealer_value.perl}";
if $dealer_value == any( $player_value ^.. 21) {
say "you lose!";
exit 0;
}
elsif $dealer_value < 21 {
my $card = @cards.shift;
@dealer.push( $card );
say $card.key;
$dealer_value += $card.value;
}
else {
say "dealer bust: you win!";
exit 0;
}
}
}
sub default-cards {
return [
"three of diamonds" => 3,
"five of diamonds" => 5,
"seven of diamonds" => 7,
"ten of diamonds" => 10,
"two of diamonds" => 2,
"jack of spades" => 10,
"five of clubs" => 5,
"five of hearts" => 5,
"eight of diamonds" => 8,
"six of spades" => 6,
"five of spades" => 5,
"king of hearts" => 10,
"nine of diamonds" => 9,
"two of hearts" => 2,
"king of clubs" => 10,
"eight of clubs" => 8,
"two of spades" => 2,
"ace of hearts" => any(1, 11),
"nine of hearts" => 9,
"eight of spades" => 8,
"jack of diamonds" => 10,
"jack of hearts" => 10,
"nine of clubs" => 9,
"ten of hearts" => 10,
"eight of hearts" => 8,
"king of spades" => 10,
"ace of spades" => any(1, 11),
"queen of hearts" => 10,
"nine of spades" => 9,
"two of clubs" => 2,
"queen of diamonds" => 10,
"three of spades" => 3,
"queen of clubs" => 10,
"three of clubs" => 3,
"ten of spades" => 10,
"ace of clubs" => any(1, 11),
"ace of diamonds" => any(1, 11),
"four of hearts" => 4,
"six of clubs" => 6,
"ten of clubs" => 10,
"seven of hearts" => 7,
"king of diamonds" => 10,
"four of diamonds" => 4,
"seven of spades" => 7,
"queen of spades" => 10,
"four of spades" => 4,
"six of hearts" => 6,
"four of clubs" => 4,
"seven of clubs" => 7,
"six of diamonds" => 6,
"three of hearts" => 3,
"jack of clubs" => 10]<>;
}