# Exercise – Making a Card Deck Type

Let's now try to implement a data type that will represent a deck of cards. First, we can think about what type would be fitting for a card deck – a list of cards would be a good representation. But then what type is fitting for a single card?

**Each card should have a rank and a suit**so we can make another type for cards that has the type of a tuple`(Rank, Suit)`

. Let's start at the lowest level, the `Rank`

and `Suit`

type. Remember that we already defined the `Suit`

type, but we will now also derive the `Show`

class for it:data Suit = Hearts

| Diamonds

| Spades

| Clubs

deriving (Show)

which leaves us with the task of defining

`Rank`

for which we can also use nullary constructors and also derive some built-in classes:data Rank = Deuce

| Three

| Four

| Five

| Six

| Seven

| Nine

| Ten

| Jack

| Queen

| King

| Ace

deriving (Show, Eq, Ord, Enum)

We can then already use methods of those classes on the

`Rank`

type:ghci> Deuce < Three

True

ghci> Deuce <= Three

True

ghci> Deuce == Three

False

ghci> Deuce > Three

False

ghci> [Deuce .. Five]

[Deuce, Three, Four, Five]

We have the

`Rank`

and `Suit`

types now, and we can simply define the type of Card as a type synonym for a tuple of `(Rank, Suit)`

:type Card = (Rank, Suit)

Similarly, we can define a deck of cards as a type synonym for a list of

`Card`

types:type Deck = [Card]

We have all the required types for actually building a deck now, so let's make a function for that purpose. We will use list comprehension and take advantage of the fact that

`Rank`

supports enumeration:buildDeck :: Deck

buildDeck = [(rank, suit) | rank <- [Deuce .. Ace], suit <- suitList]

where

suitList = [Hearts, Diamonds, Spades, Clubs]

And we can now build a deck of cards using that function:

ghci> deck = buildDeck

ghci> show deck

"[(Deuce, Hearts),(Deuce, Diamonds),(Deuce, Spades),(Deuce, Clubs),

(Three, Hearts),(Three, Diamonds),(Three, Spades),(Three, Clubs),(Four,

Hearts),(Four, Diamonds),(Four, Spades),(Four, Clubs),(Five, Hearts),

(Five, Diamonds),(Five, Spades),(Five, Clubs),(Six, Hearts),(Six,

Diamonds),(Six, Spades),(Six, Clubs),(Seven, Hearts),(Seven, Diamonds),

(Seven, Spades),(Seven, Clubs),(Nine, Hearts),(Nine, Diamonds),(Nine,

Spades),(Nine, Clubs),(Ten, Hearts),(Ten, Diamonds),(Ten, Spades),(Ten,

Clubs),(Jack, Hearts),(Jack, Diamonds),(Jack, Spades),(Jack, Clubs),

(Queen, Hearts),(Queen, Diamonds),(Queen, Spades),(Queen, Clubs),(King,

Hearts),(King, Diamonds),(King, Spades),(King, Clubs),(Ace, Hearts),(Ace,

Diamonds),(Ace, Spades),(Ace, Clubs)]"

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