Re: [Caml-list] Unwanted type constraint in mutually recursive parameterized class type definition.

[Philippe Veber <philippe.veber@gmail.com>]

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This workaround worked just fine, thanks a lot!
ph.


2015-07-09 1:57 GMT+02:00 Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>:

> On 2015/07/09 01:24, Philippe Veber wrote:
> >
> > Dear camlers,
> >
> >   I obtain an unexpected answer from the toplevel when I enter the
> following definition:
> >
> >         OCaml version 4.03.0+dev7-2015-02-08
> >
> > # class type ['a] c =
> >   object
> >     method m : d
> >   end
> > and d =
> >   object
> >     inherit [int] c
> >   end
> > ;;
> > class type ['a] c = object constraint 'a = int method m : d end
> > and d = object method m : d end
> >
> > What surprises me is the constraint 'a = int in the definition of c. Is
> this is a bug or feature?
>
>
> This is a feature (or at least, the intended behavior)
> For classes, type constraints are inferred automatically, but in a
> monomorphic way.
> A standard workaround is to open the recursion by generalizing definitions:
>
> class type ['a,'d] c0 = object method m : 'd end
> class type d = object inherit ['a,d] c0 end
> class type ['a] c = ['a,d] c0
>
> Jacques Garrigue

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