Subtle functor application bug

[vicuna]

Original bug ID: 51 Reporter: administrator Status: closed Resolution: fixed Priority: normal Severity: minor Category: ~DO NOT USE (was: OCaml general) Related to: #6651 #7192

Bug description

Hello!

I've been looking at Ocaml module system implementation recently and I discovered a little subtle bug, which appears when you try to apply a functor which is a component of a larger structure and whose type is a "module type" defined in the same structure.....

Well, to be more explicit, here is an example of a functor F with the caracteristics as described above, and the bug that is produced:

    Objective Caml version 2.04

module X=struct

module type SIG=sig type t=int val x:t end;;
module F(Y:SIG) : SIG = struct type t=Y.t let x=Y.x end;;

end;; module X : sig module type SIG = sig type t = int val x : t end module F : functor(Y : SIG) -> SIG end

module DUMMY=struct type t=int let x=2 end;;

module DUMMY : sig type t = int val x : int end

(3 : X.F(DUMMY).t);;

Unbound type constructor X.F(DUMMY).t

Apparenly the type system does not know that there is a type component "t" in the result of the application of X.F to DUMMY. The same thing works perfectly well if SIG and F are defined at toplevel:

    Objective Caml version 2.04

module type SIG=sig type t=int val x:t end;;

module type SIG = sig type t = int val x : t end

module F(Y:SIG) : SIG = struct type t=Y.t let x=Y.x end;;

module F : functor(Y : SIG) -> SIG

module DUMMY=struct type t=int let x=2 end;;

module DUMMY : sig type t = int val x : int end

(3 : F(DUMMY).t);;

• : F(DUMMY).t = 3

I haven't checked with the recent version of Ocaml, but I looked at the CVS server and I think that the error will persist...

My guess is that the functor components evaluated for X.F in the function "components_of_module", correspond to: fcomp_param = "Y" fcomp_arg = "X.SIG" fcomp_res = "X.SIG" fcomp_env = {... SIG -> sig...end ... } And since there is no "X.SIG" in fcomp_env but only SIG, the function "components_of_module_application" computes empty components structure for X.F(DUMMY).

Best regards

Jacek Chrzaszcz

-- Laboratoire de Recherche en Informatique (LRI) - Equipe DEMONS batiment 490, bureau 153, Universite Paris-Sud 91405 ORSAY (FRANCE) tel:33.1.69.15.42.35 - fax:33.1.69.15.65.86 - http://www.lri.fr/~jacek

[vicuna]

Comment author: administrator

I've been looking at Ocaml module system implementation recently and I discovered a little subtle bug, which appears when you try to apply a functor which is a component of a larger structure and whose type is a "module type" defined in the same structure.....

(3 : X.F(DUMMY).t);;

Unbound type constructor X.F(DUMMY).t

Right. Thanks for spotting that problem.

My guess is that the functor components evaluated for X.F in the function "components_of_module", correspond to: fcomp_param = "Y" fcomp_arg = "X.SIG" fcomp_res = "X.SIG" fcomp_env = {... SIG -> sig...end ... } And since there is no "X.SIG" in fcomp_env but only SIG, the function "components_of_module_application" computes empty components structure for X.F(DUMMY).

Your guess is correct. fcomp_res should be the result signature of the functor before prefixing (so that it makes sense in fcomp_env), and the prefixing substitution should be recorded in the functor_components record for prefixing when components_of_module_app computes the environment.

The working sources incorporate the fix.

All the best,

• Xavier Leroy

[vicuna]

Comment author: administrator

Fixed in 3.00