GADTs and polymorphic variants

foo.ml

(* Overly simplified example *)

type _ foo =
  | Foo : int -> [< `A | `B ] foo
  | Bar : int -> [< `B | `C ] foo

(* The most general type for foo is:
   int -> [< `A | `B ] foo
   But, because of the call in bar, the type actually inferred is:
   int -> _[< `B ] foo
*)
let rec foo i =  Foo i
and bar = [ foo 1; Bar 42 ]

(* This call then fails *)
let x : [ `A ] foo = foo 5

(* Remark: If the "rec" is dropped, the correct type for foo is inferred *)