0007834: Problem with constraints, with type, and polymorphic variants

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0007834

OCaml

typing

public

2018-07-31 17:54

2018-09-03 06:55

Reporter

lpw25

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Priority

normal

Severity

minor

Reproducibility

always

Status

new

Resolution

open

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Target Version

Fixed in Version

Summary

0007834: Problem with constraints, with type, and polymorphic variants

Description

The following code seems pretty reasonable:

  module type Q = sig
    type 'a t constraint 'a = [< `Empty | `Filled of _ ]
    module type S = sig
      type 'a t constraint 'a = [< `Empty | `Filled of _ ]
    end
    module M : S with type 'a t = 'a t
  end;;

but fails with the following error:

  Error: In this `with' constraint, the new definition of t
  does not match its original definition in the constrained signature:
  Type declarations do not match:
       type 'a t = 'a t constraint 'a = [< `Empty | `Filled of 'b & 'c & 'd ]
     is not included in
       type 'a t constraint 'a = [< `Empty | `Filled of 'b ]
     Their constraints differ.

I haven't dug into this issue properly, but I can see basically how it happens. I'm not really sure there is much we can do to fix it, I suspect it would require comparing the different `&`ed types, and that has been ruled out as a too much of a PITA before. Still I figured it was worth reporting anyway.

Issue History
Date Modified	Username	Field	Change
2018-07-31 17:54	lpw25	New Issue

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