F# pattern matching - type test

pattern_matching_with_type_test.fsx

type A() = class end
type B() = inherit A()
type C() = inherit A()

let evaluation (obj: A) =
  match obj with
  | :? B -> "It's a B"
  | :? C -> "It's a C"
  | :? A -> "It's a A"
  | _ -> "nothing"

let a = new A()
let b = new B()
let c = new C()

printfn "%s" (evaluation a)
printfn "%s" (evaluation b)
printfn "%s" (evaluation c)