F# for fun and profit - Computation Expressions - Bind exercise - http://fsharpforfunandprofit.com/posts/computation-expressions-bind/

Bind.fs

// Exercises from http://fsharpforfunandprofit.com/posts/computation-expressions-bind/
// Part 1

let strToInt str =
    match System.Int32.TryParse str with
    | (false, _) -> None
    | (true, x) -> Some x

type YourWorkflowBuilder() =
    member this.Bind(x, f) = Option.bind f x
    member this.Return(x) = Some x
let yourWorkflow = new YourWorkflowBuilder()

let stringAddWorkflow x y z =
    yourWorkflow
        {
        let! a = strToInt x
        let! b = strToInt y
        let! c = strToInt z
        return a + b + c
        }

// test
let good = stringAddWorkflow "12" "3" "2"
let bad = stringAddWorkflow "12" "xyz" "2"

// Part 2
let strAdd str i = strToInt str |> Option.bind ((+) i >> Some)
let (>>=) m f = Option.bind f m

let good' = strToInt "1" >>= strAdd "2" >>= strAdd "3"
let bad' = strToInt "1" >>= strAdd "xyz" >>= strAdd "3"