FSharpRef/Functional.fs

   1 module Functional
   2
   3 open System.IO
   4 open System.Linq
   5
   6 // Write something on a file.
   7 let appendFile (filename: string) (text: string) =
   8     use sw = new StreamWriter(filename, true)
   9     sw.WriteLine(text)
  10
  11 // Recursive function.
  12 let rec fac n =
  13     if n <= 1 then 1
  14     else n * fac (n - 1)
  15
  16 // Mutual recursive functions.
  17 let rec isEven n =
  18     if n = 0 then true
  19     elif n = 1 then false
  20     else isOdd (n - 1)
  21 and isOdd n =
  22     if n = 0 then false
  23     elif n = 1 then true
  24     else isEven (n - 1)
  25
  26 // Algebraic data type.
  27 type Suit =
  28     | Diamond
  29     | Spade
  30     | Heart
  31     | Club
  32
  33 type PlayingCard =
  34     | Ace of Suit
  35     | King of Suit
  36     | Queen of Suit
  37     | Jack of Suit
  38     | NumCard of int * Suit
  39     member this.Value = // Property.
  40         match this with
  41             | Ace (_) -> 14
  42             | King (_) -> 13
  43             | Queen (_) -> 12
  44             | Jack (_) -> 11
  45             | NumCard (n, _) when n >= 2 && n <= 10 -> n
  46             | NumCard (_) -> failwith "Card has invalid value!"
  47
  48 let deckOfCards =
  49     [
  50         for suit in [ Spade; Club; Heart; Diamond ] do
  51             yield Ace(suit)
  52             yield King(suit)
  53             yield Queen(suit)
  54             yield Jack(suit)
  55             for n in [2 .. 10] do
  56                 yield NumCard(n, suit)
  57     ]
  58
  59 // Records with custom equality.
  60 [<CustomEquality; NoComparison>]
  61 type Person =
  62     { First: string; Last: string; Age: int }
  63     override this.Equals(other) =
  64         match other with
  65         | :? Person as p -> p.First = this.First && p.Last = this.Last
  66         | _ -> false
  67     override this.GetHashCode() =
  68         this.First.GetHashCode() ^^^ this.Last.GetHashCode()
  69
  70 let steve = { First = "Steve"; Last = "Holt"; Age = 17 }
  71 let stevesTwin = { steve with First = "Paul" }
  72
  73 // Queries. Should be used with SQL or other external data sources.
  74 let youngPersonNames persons =
  75    query {
  76       for p in persons do
  77       where (p.Age < 15)
  78       select p.First
  79    }
  80
  81 // Infinite lazy sequence.
  82 let allPositiveInts =
  83     seq {
  84         for i in 1 .. System.Int32.MaxValue do
  85             yield i
  86     }
  87 let rec fibs x y =
  88    seq {
  89       yield x
  90       yield! fibs y (x + y)
  91    }
  92 let testYieldBang =
  93     seq {
  94         yield 10
  95         yield! [1; 2; 3] // Yields a collection.
  96     }
  97 // Generator.
  98 let testUnfold =
  99     Seq.unfold (fun a -> if a > 10 then None else Some(10 * a, a + 1)) 1
 100
 101 // Functions composition.
 102 let SizeOfFolder =
 103     let getFiles folder =
 104         Directory.GetFiles(folder, "*.*", SearchOption.AllDirectories)
 105     getFiles
 106     >> Array.map (fun file -> (new FileInfo(file)).Length)
 107     >> Array.sum
 108
 109 // Matches literals.
 110 [<Literal>]
 111 let Bill = "Bill Gates" // Must begin with a capital!
 112 let greet name =
 113    match name  with
 114    | Bill -> "Hello rich Bill!"
 115    | name -> sprintf "Hello poor %s" name
 116
 117 // Matches tuples.
 118 let testXor x y =
 119    match x, y with
 120    | a, b when a <> b -> true
 121    | _ -> false