Representing playing cards as specifications

A playing card has a face value and a suit. There are 4 suits in a card deck.

A specification for the possible suits can be defined using literal values

(spec/def ::suits #{:clubs :diamonds :hearts :spades})

As the set is a predicate then it could just be bound to a name, i.e. (def suits? #{:clubs :diamonds :hearts :spades})

Representing different aspects of card game decks

Suits from different regions are called by different names. Each of these suits can be their own spec.

(spec/def ::suits-french #{:hearts :tiles :clovers :pikes})

(spec/def ::suits-german #{:hearts :bells :acorns :leaves})

(spec/def ::suits-spanish #{:cups :coins :clubs :swords})

(spec/def ::suits-italian #{:cups :coins :clubs :swords})

(spec/def ::suits-swiss-german #{:roses :bells :acorns :shields})

A composite specification called ::card-suits provides a simple abstraction over all the variations of suits. Using ::card-suits will be satisfied with any region specific suits.

(spec/def ::card-suits
  (spec/or :french ::suits-french
           :german ::suits-german
           :spanish ::suits-spanish
           :italian ::suits-italian
           :swiss-german ::suits-swiss-german
           :international ::suits-international))

Define an alias for a specification

Jack queen king are called face cards in the USA and occasionally referred to as court cards in the UK.

Define a spec for ::face-cards and then make ::court-cards and alias for ::face-cards

(spec/def ::face-cards #{:jack :queen :king :ace})

(spec/def ::court-cards ::face-cards)

Any value that conforms to the ::face-card specification also conforms to the ::court-cards specification.

(spec/conform ::court-cards :ace)

Playing card rank

Each suit in the deck has the same rank of cards explicitly defining a rank

(spec/def ::rank #{:ace 2 3 4 5 6 7 8 9 10 :jack :queen :king})

rank can be defined more succinctly with the clojure.core/range function. The expression (range 2 11) will generates a sequence of integer numbers from 2 to 10 (the end number is exclusive, so 11 is not in the sequence).

Using clojure.core/into this range of numbers can be added to the face card values.

(into #{:ace :jack :queen :king} (range 2 11))

The ::rank specification now generates all the possible values for playing cards.

(spec/def ::rank (into #{:ace :jack :queen :king} (range 2 11)))

The specification only checks to see if a value is in the set, the order of the values in the set is irrelevant.

Playing Cards

A playing card is a combination of suit and face value, a pair of values, referred to as a tuple.

Clojure spec has a tuple function, however, we need to define some predicates first

(spec/def ::playing-card (spec/tuple ::rank ::suits ))

Use the spec with values to see if they conform. Try you own values for a playing card.

(spec/conform ::playing-card [:ace :spades])