Original bug ID: 1382
Reporter: administrator
Status: closed
Resolution: fixed
Priority: normal
Severity: minor
Category: ~DO NOT USE (was: OCaml general)
Related to: #3652
Parent of: #3655

Bug description

Hmm, this email bounced the first time. Try #2.

Here's 60 lines of source code that breaks the current ocamlc from
CVS. Sorry I can't make it smaller.

It may be significant that the error message ends up mentioning

< format_eventid_tag : 'a. ([> `ANY] as 'b) Conscious.CD.eventid -> unit >

when in the actual code, the type variable argument to
format_eventid_tag is always equal to the type variable in the first
argument. That is, the 'a and 'b should not be different in the
above.

When I have shuffled text so it is less than 3 files, the problem
went away. To reproduce the problem, give these commands:

ocamlc -c conscious_data.ml
ocamlc -c conscious.ml
ocamlc -c ouch.ml

and you'll get this compiler error:

File "ouch.ml", line 9, characters 22-155:
Signature mismatch:
Modules do not match:
sig
class ['a] structure_read_desc :
object
constraint 'a = [> ANY] method dump : Conscious.CD.formatter -> string array -> unit end end is not included in Event Class declarations do not match: class ['a] structure_read_desc : object constraint 'a = [> ANY]
method dump : Conscious.CD.formatter -> string array -> unit
end
does not match
class ['a] structure_read_desc :
object
constraint 'a = [> ANY] method dump : CD.formatter -> string array -> unit end The class type object method dump : Conscious.CD.formatter -> string array -> unit end is not matched by the class type object method dump : CD.formatter -> string array -> unit end The method dump has type Conscious.CD.formatter -> string array -> unit but is expected to have type CD.formatter -> string array -> unit Type Conscious.CD.formatter = < format_eventid_tag : 'a. ([> ANY] as 'b) Conscious.CD.eventid -> unit >
is not compatible with type
CD.formatter =
< format_eventid_tag : 'c. ([> `ANY] as 'c) CD.eventid -> unit >
Type 'b Conscious.CD.eventid = 'b Conscious_data.Conscious_data.eventid
is not compatible with type
'c CD.eventid = 'c Conscious_data.Conscious_data.eventid

ouch.ml contains:

module CD = Conscious_data.Conscious_data
module C = Conscious.Conscious

module type Event = sig
class ['a] structure_read_desc: [[>`ANY] as 'a] CD.eventdesc
end

(* The : Event is essential to reproducing the problem. *)
module Event: Event = struct

class ['a] structure_read_desc =
object
inherit ['a] C.scalar_eventdesc_impl
method dump f bva = failwith "ouch"
end

end

conscious_data.ml contains:

module type Conscious_data = sig
type 'a eventid

class type formatter =
object
(* The type constraint [>ANY] as 'a is essential to aggravate the problem. *) method format_eventid_tag: 'a . ([>ANY] as 'a) eventid -> unit
end

class type ['a] eventdesc = object
method dump: formatter -> string array -> unit
end

end

(* If I eliminate the :Conscious_data on the next line, the problem goes
away. *)
module Conscious_data: Conscious_data = struct

type 'a eventid = int

class type formatter =
object
method format_eventid_tag: 'a . ([>`ANY] as 'a) eventid -> unit
end

class type ['a] eventdesc = object
method dump: formatter -> string array -> unit
end

end

and conscious.ml contains:

module CD = Conscious_data.Conscious_data
module Conscious = struct

 class virtual ['a] scalar_eventdesc_impl =
 object (self: 'self)
   constraint 'a = [>`ANY]
   method virtual dump: CD.formatter -> string array -> unit
   constraint 'self = [>`ANY] #CD.eventdesc
 end

end

--
Tim Freeman
tim@fungible.com
GPG public key fingerprint ECDF 46F8 3B80 BB9E 575D 7180 76DF FE00 34B1 5C78