MaybeMonad.fs

(* Maybe Monad *)
(* 
   Taken from FSharpX: 
   https://github.com/fsprojects/fsharpx/blob/master/src/FSharpx.Core/ComputationExpressions/Monad.fs
*)
type MaybeBuilder() =
   member this.Return(x) = Some x
   member this.ReturnFrom(m: 'T option) = m
   member this.Zero() = None
   member this.Bind(m, f) = Option.bind f m
   
let maybe = MaybeBuilder()

let res =
   maybe {
      let! x1 = Some(10)       // maybe.Bind(Some(10), fun a -> 
      let! x2 = None           //    maybe.Bind(None, fun b ->
      return! Some(x1 + x2)    //       a + b Using Option 
   }

printf "%A" res