[Caml-list] a question about Ocaml semantics

[Matej Kosik <5764c029b688c1c0d24a2e97cd764f@gmail.com>]

Hi,

There's an Ocaml language feature I do not understand.

E.g. in this example:

  type 'a phantom = int
  type t = { enter : 'a. 'a phantom -> int }
  let f g = g.enter 2
  let _ = f { enter = fun x -> 1 + x } (* ok *)
  let _ = f { enter = (+) 1 }          (* fails to typecheck *)

I don't get why, if we have:

  type 'a phantom = int

i.e. "'a phantom" is defined as an alias of "int",
how is it possible that the following types:

  { enter : 'a. 'a phantom -> int }

is not equal to

  { enter : 'a. int -> int }

I've tried to find a corresponding section in the Reference Manual, but I failed.
Where is this explained?