[Caml-list] Problem of type equality in a single definition (was: In 3.12 and 4.0, erratic message "The implementation tt.ml does not match the interface tt.cmi")

[Jean-Louis Giavitto <jean-louis.giavitto@ircam.fr>]

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Dear all,
I have circumscribed my initial problem and I am able to produce it on a 
simple case.


I have a signature Classdef.mli restrcted to

   class virtual ['a, 'b, 'c] cl0 :
   object
     constraint 'c = < m : 'a -> 'b -> int; .. >
   end

   class virtual ['a, 'b] cl1 :
   object
     method virtual m : 'a -> 'b -> int
     method virtual raise_trouble : 'a
   end

   class virtual ['a, 'b] cl2 :
   object
     method virtual as_cl0 : ('a, 'b, ('a, 'b) cl1) cl0
   end

then, in another module that contains only the following type declaration

   type refer =
     {
       poly : 'a 'b 'c . (('b, 'c) #Classdef.cl2 as 'a);
     }

raise the error:

  File "anotherModule.ml", line 1, characters 0-1:
  Error: The implementation anotherModule.ml
        does not match the interface (inferred signature):
        Type declarations do not match:
          type refer = { poly : 'a 'b 'c. ('b, 'c) #Classdef.cl2 as 'a; }
        is not included in
          type refer = { poly : 'a 'b 'c. ('b, 'c) #Classdef.cl2 as 'a; }
        The types for field poly are not equal.


Note that
- if I suppress the method raise_trouble
- or if neither 'a nor 'b appear in the type of this method,
then everything works fine.

Can someone explain to me this behavior? (the two files are in the 
attached tarball):
. First, I don't understand which instances of type poly are compared:
   there is only one single definition of this type and no use.
. And second, I don't understand why adding a method will change the
   behavior.

Many thanks in advance,
Jean-Louis Giavitto



-------------------------------------------------------
Le 22/07/64 20:59, Jean-Louis Giavitto a écrit :
> Hello.
> if anyone could give me some hints on the following problem...
>
>
> I have a file tt.ml which reduces to
>
> type typedef = {
> isa : 'a 'rep 'cell .
> (('rep, int, int, int, int, int) #Collection.collection as 'a);
> }
>
> The mli file is exactly the same has the ml file. 'collection' is a
> virtual class declared in file collection.ml and signature in
> collection.mli.
>
> tt.ml compile without problems. However, if I replace (in tt.ml and
> tt.mli) one of the 'int' parameter by a type variable:
>
> type typedef = {
> isa :
> 'a 'rep 'cell .
> (('rep, 'cell, int, int, int, int) #Collection.collection
> as 'a);
> }
>
> then I have the following message (with the 4.0 compiler):
>
> File "tt.ml", line 1:
> Error: The implementation tt.ml does not match the interface tt.cmi:
> Type declarations do not match:
> type typedef = {
> isa :
> 'a 'rep 'cell.
> ('rep, 'cell, int, int, int, int) #Collection.collection as 'a;
> }
> is not included in
> type typedef = {
> isa :
> 'a 'rep 'cell.
> ('rep, 'cell, int, int, int, int) #Collection.collection as 'a;
> }
> File "tt.ml", line 2, characters 5-112: Actual declaration
> The types for field isa are not equal.
>
>
> - The problem appears with the compiler 3.12 but also 4.0 (a similar
> error (5622) was reported but was not reproducible with 4.0).
> - I have no problem if I drop the .mli file.
> - The error seems sensitive to the definition of the class 'collection':
> I was not able to reproduce it with a much simpler definition of
> collection.
> - I have the same error if I replace more 'int' parameter by type
> variables.
>
> Have you any clues?
> Jean-Louis Giavitto.


-- 
Jean-Louis Giavitto
Ircam CNRS UMR STMS 9912 – UPMC – Inria
1, place Igor Stravinsky, 75004 Paris

http://repmus.ircam.fr/giavitto
http://mgs.spatial-computing.org

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