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Loop Unrolling

C++ style metaprogramming in F#

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type Peano = interface end
and Zero = Zero with
    static member inline (|*|) (f, Zero) = f $ Zero
    interface Peano
and Succ<'a when 'a :> Peano> = Succ of 'a  with
    static member inline (|*|) (f, Succ(x)) = f $ Succ(x) 
    interface Peano


type PeanoToInt = PeanoToInt with
    static member inline ($) (PeanoToInt, Zero) = 0
    static member inline ($) (PeanoToInt, Succ (x)) = 1 + (PeanoToInt |*| x)

type Repeat = Repeat with
    static member inline ($) (Repeat, Zero) = fun f -> ()
    static member inline ($) (Repeat, (Succ (x) as p)) = fun f ->
        (Repeat |*| x) f
        f (PeanoToInt $ p) 

let four = Succ (Succ (Succ (Succ Zero)))
let inline repeat step f = (Repeat $ step) f

// Examples

repeat four (fun index -> printfn "index: %d" index)

// zero-out
let array = [|1..8|]
for i in 0 .. 4 .. array.Length - 1 do
    repeat four (fun index -> array.[i + (index - 1)] <- 0)
Multiple items
union case Zero.Zero: Zero

--------------------
type Zero =
  | Zero
  interface Peano
  static member ( |*| ) : f:'a * Zero:Zero -> '_arg5 (requires member ( $ ))

Full name: Script.Zero
val f : 'a (requires member ( $ ))
type Peano

Full name: Script.Peano
Multiple items
union case Succ.Succ: 'a -> Succ<'a>

--------------------
type Succ<'a (requires 'a :> Peano)> =
  | Succ of 'a
  interface Peano
  static member ( |*| ) : f:'a0 * Succ<'b> -> '_arg8 (requires member ( $ ) and 'b :> Peano)

Full name: Script.Succ<_>
val f : 'a (requires member ( $ ) and 'b :> Peano)
val x : #Peano
Multiple items
union case PeanoToInt.PeanoToInt: PeanoToInt

--------------------
type PeanoToInt =
  | PeanoToInt
  static member ( $ ) : PeanoToInt:PeanoToInt * Zero:Zero -> int
  static member ( $ ) : PeanoToInt:PeanoToInt * Succ<'a> -> int (requires 'a :> Peano and member ( |*| ))

Full name: Script.PeanoToInt
val x : 'a (requires 'a :> Peano and member ( |*| ))
Multiple items
union case Repeat.Repeat: Repeat

--------------------
type Repeat =
  | Repeat
  static member ( $ ) : Repeat:Repeat * Zero:Zero -> ('a -> unit)
  static member ( $ ) : Repeat:Repeat * Succ<'a> -> ((int -> 'b) -> 'b) (requires 'a :> Peano and member ( |*| ) and member ( |*| ))

Full name: Script.Repeat
val f : 'a
val x : 'a (requires 'a :> Peano and member ( |*| ) and member ( |*| ))
val p : Succ<'a> (requires 'a :> Peano and member ( |*| ) and member ( |*| ))
val f : (int -> 'b)
val four : Succ<Succ<Succ<Succ<Zero>>>>

Full name: Script.four
val repeat : step:'a -> f:'b -> 'c (requires member ( $ ))

Full name: Script.repeat
val step : 'a (requires member ( $ ))
val f : 'b
val index : int
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn
Multiple items
val array : int []

Full name: Script.array

--------------------
type 'T array = 'T []

Full name: Microsoft.FSharp.Core.array<_>
val i : int
property System.Array.Length: int
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More information

Link:http://fssnip.net/hW
Posted:3 years ago
Author:Nick Palladinos
Tags: metaprogramming