Assignment_07-FSharp/Assignment_07-FSharp/Program.fs

   1 open System
   2
   3 // Question 1.
   4 type Stack<'a> =
   5     | Elem of 'a * Stack<'a>
   6     | Empty
   7     member this.Push a = Elem (a, this)
   8     member this.Top =
   9         match this with
  10         | Elem (a, _) -> a
  11         | Empty -> failwith "Empty stack!"
  12     member this.Pop =
  13         match this with
  14         | Elem (_, rest) -> rest
  15         | Empty -> failwith "Empty stack!"
  16     override this.ToString () =
  17         match this with
  18         | Elem (e, rest) -> e.ToString() + "," + rest.ToString()
  19         | Empty -> "Empty"
  20
  21 type Foo () = class end
  22 type Bar () = inherit Foo ()
  23
  24 let question1 () =
  25     printfn "Question 1"
  26     let a = (((Empty.Push "hello").Push "world").Push "it's fun").Pop
  27     printfn "a: %O" a
  28     assert (a.ToString () = "world,hello,Empty")
  29
  30     let b = ((Empty.Push 1).Push 3)
  31     printfn "b.Top: %O" b.Top
  32     assert (b.Top = 3)
  33
  34     let c : Stack<Bar> = (Empty.Push <| Bar ()).Push <| Bar ()
  35     c.Top :> Bar |> ignore
  36     c.Top :> Foo |> ignore
  37
  38     let d : Stack<#Foo> = (Empty.Push <| Bar ()).Push <| Bar ()
  39     d.Top :> Bar |> ignore
  40
  41 // Question 4.
  42 let question4 () =
  43     let rec sieve sequence =
  44         seq {
  45             let h = Seq.head sequence
  46             yield h
  47             yield! sieve <| Seq.filter (fun m -> m % h <> 0) sequence
  48         }
  49     let primes = sieve <| (Seq.initInfinite id |> Seq.skip 2)
  50     printfn "first primes: %A" <| (Seq.take 100 primes |> Seq.toList)
  51
  52 [<EntryPoint>]
  53 let main argv =
  54     question1 ()
  55     question4 ()
  56     0
  57