0004569: Conjunctive polymorphic variants in class parameter constraints are rejected

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Date Submitted

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0004569

OCaml

OCaml general

public

2008-06-25 05:02

2008-06-25 05:06

Reporter

garrigue

Assigned To

Priority

normal

Severity

minor

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

3.10.2

Target Version

Fixed in Version

3.10.3+dev

Summary

0004569: Conjunctive polymorphic variants in class parameter constraints are rejected

Description

Reported by Khoo Yit Phang on the caml list 2008-06-24:

I discovered that the attached snippet of Ocaml does not compile in
ocamlc, but does work in the ocaml toplevel (tested in v3.10.0 and
3.10.2). Removing anything (except the :int annotation) causes the
error to go away. Is it a bug in the type-checker?

# cat polymorphic-variants-methods-bug.ml
class ['a] c (a : 'a) =
    object (s)
        method s = s
        method d : int = match a with `A b -> b#num
    end

# ocamlc polymorphic-variants-methods-bug.ml
The implementation polymorphic-variants-methods-bug.ml
does not match the interface (inferred signature):
Type declarations do not match:
  type 'a c = < d : int; s : 'a c >
    constraint 'a = [< `A of < num : int; .. > & < num : int; .. > ]
is not included in
  type 'a c = < d : int; s : 'a c >
    constraint 'a =
      [< `A of < num : int; .. > & < num : int; .. > & < num : int; ..
> ]

#ocamlc -i polymorphic-variants-methods-bug.ml
class ['a] c :
  'a ->
  object ('b)
    constraint 'a = [< `A of < num : int; .. > ]
    method d : int
    method s : 'b
  end

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Notes
(0004524) garrigue (manager) 2008-06-25 05:06	This was due to the way unification is used during type expansion. Fxied in branch release310 by making the unification rigid when expanding a type during an equality check.

Issue History
Date Modified	Username	Field	Change
2008-06-25 05:02	garrigue	New Issue
2008-06-25 05:06	garrigue	Status	new => closed
2008-06-25 05:06	garrigue	Note Added: 0004524
2008-06-25 05:06	garrigue	Resolution	open => fixed
2008-06-25 05:06	garrigue	Fixed in Version	=> 3.10.3+dev