dbrattli

module Promise =
    let sleep msecs =
        let promise = Promise<unit> ()
        let timer = new System.Timers.Timer (float msecs)
        timer.AutoReset <- false

        let eventHandler ev =
            promise.Resolve ()

        timer.Elapsed.Add eventHandler

dbrattli

let pr = Promise ()
pr.Catch (fun err -> printfn "Got Exception: %A" (err.ToString ())) |> ignore

pr.Reject (Exception "error")

dbrattli

let pr = Promise ()
pr.Then (fun x -> printfn "Got value: %A" x) |> ignore

pr.Resolve 42

dbrattli

type Promise<'a> () =
    let mutable result : Result<'a, exn> option = None
    let thenCbs = List<Callback<'a>> ()
    let catchCbs = List<Callback<exn>> ()

    member this.Resolve (value: 'a) =
        result <- Some <| Ok value
        for cb in thenCbs do
            cb value

dbrattli

// Return a function that takes a callback that takes the result.
let times10 (x: int) : ((int -> unit) -> unit) =
    let thenDo (cb : int -> unit) =
        cb  (x * 10)
    thenDo

let cb result =
    printfn "%A" result

let thenDo = times10 42

dbrattli

let times10 (x : int) (cont : int -> unit) : unit =
    cont (x * 10)

let cb result =
    printfn "%A" result

do times10 42 cb

dbrattli

// Unindented Pythagoras CPS
let pythagorasCps a b return' : unit =
    squareCps a (fun aa ->
    squareCps b (fun bb ->
    addCps aa bb (fun aabb ->
    sqrtCps aabb (fun result ->
    return' result))))

dbrattli

// Pythagoras rewritten using 'let' statements
let pythagoras a b =
    let aa = square a
    let bb = square b
    let aabb = add aa bb
    let result = sqrt aabb
    result
    

dbrattli

let addCps a b cont : unit =
    cont (a + b)

let squareCps x cont : unit =
    cont (x * x)

let sqrtCps x cont : unit =
    cont (sqrt x)

// Pythagoras rewritten in CPS

dbrattli

let add a b = a + b
let square x = x * x
let pythagoras a b = sqrt (add (square a) (square b))

let result = pythagoras 10.0 20.0