Maybe

Maybe.fs

type MaybeBuilder() =
    
    member this.Bind(m,f) = Option.bind f m

    member this.Return(m) = Some(m)

let maybe = MaybeBuilder()

// Returns Some (querystring) or None if the let! returns None.
let queryString = 
  maybe {
    let! val = x.Query
    return val
           |> Seq.map (fun (k,v) -> k + "=" + v)
           |> String.concat "&"
           |> (+) "?"`
  }