Program.fs

type Polynominal<'a>(x : 'a) =
    static member op_Implicit (x : 'a) = Polynominal x

type Rational<'a>(x : 'a) =
    class end

let x : Rational<Polynominal<float>> = Rational 1.0

printfn "%A" x

Generic Mathにからめて、こういうコードの方が良かっただろうか

type Polynominal<'a>(x : 'a list) =
    static member inline One with get () = Polynominal [LanguagePrimitives.GenericOne]

type Rational<'a>(x : 'a, y : 'a) =
    static member inline from x = Rational (x, LanguagePrimitives.GenericOne)

let x = Rational (3, 5)                      // 3 / 5
let y = Rational<_>.from 2.5                 // 2.5 / 1.0
let z = Rational<_>.from (Polynominal [4.2]) // Polynominal [4.2] / Polynominal [1.0]