Question

I am working on an F# tutorial that creates a deck of cards. The types are listed, but I cannot understand how to loop through the types to create the map of the full deck. I expected to do something like

Foreach rank in ranks
   Foreach suit in suits
       somehow combine the two
   next suit
next rank

Is there no way to do this? Below are the types created.

I think if I changed them from types to lists they could union, right? So, what’s the point of types?

type suits=
    |Spade=1
    |Heart=2
    |Club=3
    |Diamond=4

type ranks=
    |ValCard of int
    |Jack 
    |Queen
    |King

type deck= Deck of ranks * suits

Answer 1

Enums is a good choice for representing cards. You have comparison among suits and among ranks for free, and easily convert enums from/to int.

type suit =
    | Spade = 1
    | Heart = 2
    | Club = 3
    | Diamond = 4

type rank = 
    | Ace = 1 | Two = 2 | Three = 3 | Four = 4 | Five = 5 | Six = 6 | Seven = 7 
    | Eight = 8 | Nine = 9 | Ten = 10 | Jack = 11 | Queen = 12 | King = 13

/// 'Card' is a type which represents a particular card     
type Card = Card of rank * suit

/// 'deck' is a list consisting of all cards in a full deck
let deck = [ for r in 1..13 do
               for s in 1..4 do
                 yield Card(enum<rank> r, enum<suit> s) ]

If you go for discriminated unions, you have to manually make lists of all suits and all ranks. The advantage is better pattern matching of DUs than that of enums.

type suit =
    | Spade
    | Heart
    | Club
    | Diamond

type rank = | Ace | Two | Three | Four | Five | Six | Seven 
            | Eight | Nine | Ten | Jack | Queen | King

type Card = Card of rank * suit

let private suits = [Spade; Heart; Club; Diamond]
let private ranks = [Ace; Two; Three; Four; Five; Six; Seven; 
                     Eight; Nine; Ten; Jack; Queen; King]

let deck = [ for rank in ranks do
               for suit in suits do
                 yield Card(rank, suit) ]