BindMany.fsx

type Result<'T> =
    | Success of 'T
    | Failure of string

let bind f = function | Success a -> f a | Failure b -> Failure b
let map f = function | Success a -> Success (f a) | Failure b -> Failure b

let private combine2 fn2 fn1 arg =
    match (fn1 arg, fn2 arg) with
    | Success a, Success b -> Success (a, b)
    | Failure a, Success _ -> Failure a
    | Success _, Failure b -> Failure b
    | Failure a, Failure b -> Failure <| a + " " + b

type Combiner = Combiner with
    static member inline (?<-) (_, _, (fn1, fn2)) =
        fn1 |> combine2 fn2
    static member inline (?<-) (_, _, (fn1, fn2, fn3)) =
        fn1 |> combine2 fn2 |> combine2 fn3
        >> map (function | (a, b), c -> a, b, c)
    static member inline (?<-) (_, _, (fn1, fn2, fn3, fn4)) =
        fn1 |> combine2 fn2 |> combine2 fn3 |> combine2 fn4
        >> map (function | ((a, b), c), d -> a, b, c, d)
    static member inline (?<-) (_, _, (fn1, fn2, fn3, fn4, fn5)) =
        fn1 |> combine2 fn2 |> combine2 fn3 |> combine2 fn4 |> combine2 fn5
        >> map (function | (((a, b), c), d), e -> a, b, c, d, e)
    static member inline (?<-) (_, _, (fn1, fn2, fn3, fn4, fn5, fn6)) =
        fn1 |> combine2 fn2 |> combine2 fn3 |> combine2 fn4 |> combine2 fn5 |> combine2 fn6
        >> map (function | ((((a, b), c), d), e), f -> a, b, c, d, e, f)
    static member inline (?<-) (_, _, (fn1, fn2, fn3, fn4, fn5, fn6, fn7)) =
        fn1 |> combine2 fn2 |> combine2 fn3 |> combine2 fn4 |> combine2 fn5 |> combine2 fn6 |> combine2 fn7
        >> map (function | (((((a, b), c), d), e), f), g -> a, b, c, d, e, f, g)

let inline bindMany funs = (?<-) Combiner () funs

let succeed x = Success x
let fail i x = sprintf "failed%d" i |> Result<int>.Failure

let test = 42 |> bindMany (fail 1, fail 2, fail 3, fail 4, fail 5, fail 6, fail 7)