[Caml-list] Match error with abstract types in modules

["David Allsopp" <dra-news@metastack.com>]

Please could someone remind me what it is about types in modules which means
that

  module Foo = struct
    type 'a foo
  end

  type _ t = A : int Foo.foo t
           | B : float Foo.foo t

  let foo A = ()

is non-exhaustive pattern matching, but:

  type 'a bar

  type _ u = C : int bar u
           | D : float bar u

  let bar C = ()

is exhaustive? Or is it actually a bug (given that foo B is a type error)?


David