FSharpRef/Functional.fs

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