Version française
Home     About     Download     Resources     Contact us    

This site is updated infrequently. For up-to-date information, please visit the new OCaml website at

Browse thread
Recursive module and class
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: 2008-07-10 (13:43)
From: Jun Furuse <jun.furuse@g...>
Subject: Recursive module and class

Sorry if the following is already a known issue.

The following program trying to define a type and a class mutually recursive
is rejected by ocamlc (3.11+dev12 Private_abbrevs+natdynlink (2008-02-29)):

       module rec M : sig
         type t = Foo of N.c
       end = struct
         type t = Foo of N.c
       end and N : sig
         class c : object method x : M.t end
       end = struct
         class c = object (self)
           method x = M.Foo (self :> c)

The error message is puzzling:

       Error: Signature mismatch:
              Modules do not match:
                sig class c : object method x : M.t end end
              is not included in
                sig class c : object method x : M.t end end
              Type declarations do not match:
                type c = N.c
              is not included in
                type c = < x : M.t >

These signatures are literaly same, but do not match.

The above code is accepted by the compiler if I write

           method x = M.Foo (self :> N.c)

to coerce the object to the outer class N.c instead of c.

Is it a bug of typing? Or is it ok but with a puzzling error message ?