A simple Process MOnad in F#

Process F# Monad

type Process<'a> =
    | Value of 'a
    | Message of string

let quad a = a * a
let add a b = a + b
let print m =
    match m with
    | Value n -> printf "Number: %d\n" n
    | Message m -> printf "Message: %s\n" m
    m
let validateNumber a =
    match a with
    | even when a % 2 = 0 -> Value a
    | _ -> Message "Should be an even number!"

// map :: (a -> b) -> (a -> Mb)
let map f d =
    Value (f d)

// bind :: Ma -> (a -> Mb) -> Mb
let bind f d =
    match d with
    | Value i -> f i
    | m -> m

let p = (map quad) >> (bind validateNumber) >> print
p 2
p 3