What's the right way to check if two variants have the same ctor, but
not necessarily the same values in the ctor parms?

For example, I want to check if both data_types are Strings:

type data_type =
    String of string
  | Float of float

let a = String "foo"
let b = String "bar"
let c = Float 2.0

let ctor_equal a b = ???

ctor_equal a b = true
ctor_equal a c = false

I can think of a couple definitions of ctor_equal, one using
Hashtbl.hash_param 1 1 and one using Obj.tag (which both appear to be
doing the same thing).  Both of these seem a bit cheesy and
implementation dependent.

Is there a better way?

Chris

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