Pervasives.compare is fine for nullary constructors or where you don't mind the performance hit of the function recursing into the structure of the arguments.

A more efficient equality predicate that is really just a cut down version of [compare]:

module Kludge =
  struct
    let cmp (a: 't) (b: 't) =
      let a' = Obj.repr a and b' = Obj.repr b in
      match Obj.is_block a', Obj.is_block b' with
      | true,true ->
          Obj.tag a' = Obj.tag b'
      | false,false ->
          a' = b'
      | _ -> false
  end

It of course relies on the physical representation of sum types.
It has the merit of working on a type of any number of constructors, but the mis-merit of also operating over functions for instance!
To constrain such a comparison to sum types would require it to be built into the compiler.

Chris Q.
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