The DistributionMonad in F#

gistfile1.fs

type 'a Outcome = {
    Value: 'a
    Probability : BigRational  }

type 'a Distribution = 'a Outcome seq

// P(A AND B) = P(A | B) * P(B)
let bindD (dist:'a Distribution) (f: 'a -> 'b Distribution) =
    dist 
        |> Seq.map (fun p1 -> 
                f p1.Value
                |> Seq.map (fun p2 -> 
                        { Value = p2.Value; 
                            Probability = 
                              p1.Probability * p2.Probability}))
        |> Seq.concat : 'b Distribution

let returnD (value:'a) : 'a Distribution =   
    Seq.singleton { Value = value ; Probability = 1N/1N }