fsharp free monad proto

free.fs

// Learn more about F# at http://fsharp.net
// See the 'F# Tutorial' project for more help.

type Prj<'a> = Async<Option<'a>>

type ProjectBuilder() =
    member this.Bind(x, f) =
        async{
            let! x = x
            match x with
            | Some(x) -> return! f(x)
            | _ -> return None
        }
    member this.Return(x) = async.Return(Some x)

let proj = ProjectBuilder()

let op () = async.Return(Some(1))

[<EntryPoint>]
let main argv = 
    let r = proj{
        let! a = op()
        return a
    }
    
    printfn "%A" <| Async.RunSynchronously r
    0 // return an integer exit code