From: Jeremy Yallop <jeremy.yallop@ed.ac.uk>
To: caml users <caml-list@inria.fr>
Subject: Recursive modules and variance
Date: Thu, 26 Jun 2008 20:54:57 +0100 [thread overview]
Message-ID: <4863F411.4030701@ed.ac.uk> (raw)
Should variance annotations be visible to modules in the same recursive
group?
The following program is accepted by OCaml 3.10.2
module M : sig type +'a t end =
struct type +'a t end
module N : sig type +'a t = 'a M.t end =
struct type +'a t = 'a M.t end
but the following program is rejected
module rec M : sig type +'a t end =
struct type +'a t end
and N : sig type +'a t = 'a M.t end =
struct type +'a t = 'a M.t end
with the message
"In this definition, expected parameter variances are not satisfied.
The 1st type parameter was expected to be covariant,
but it is invariant"
Jeremy.
reply other threads:[~2008-06-26 19:55 UTC|newest]
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