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Re: [Caml-list] Can we have more flexible destructive type substitution?
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Jacques Garrigue
Jul 24, 2015, 10:37:38 AM7/24/15
to Ben Millwood, OCaML List Mailing
On 2015/07/24 23:25, Ben Millwood wrote:
>
> Currently, for [sig ... end with type lhs := rhs] to be valid, rhs needs to be an application of a type constructor to the same type parameters as lhs.
>
> I'd like to do, at a minimum, [sig ... end with type 'a t := 'a], but this is currently forbidden. Are there conceptual obstacles to permitting arbitrary type expressions on the RHS, or are they simply not implemented yet?
I think there is no problem in theory.
The reason it is not allowed currently is that substitution relies on the path substitution code, which allows only replacing a path by another path.
Would have to think about how much new code this would require to implement. It might not be that much in practice.
Jacques Garrigue
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>
> Currently, for [sig ... end with type lhs := rhs] to be valid, rhs needs to be an application of a type constructor to the same type parameters as lhs.
>
> I'd like to do, at a minimum, [sig ... end with type 'a t := 'a], but this is currently forbidden. Are there conceptual obstacles to permitting arbitrary type expressions on the RHS, or are they simply not implemented yet?
I think there is no problem in theory.
The reason it is not allowed currently is that substitution relies on the path substitution code, which allows only replacing a path by another path.
Would have to think about how much new code this would require to implement. It might not be that much in practice.
Jacques Garrigue
--
Caml-list mailing list. Subscription management and archives:
https://sympa.inria.fr/sympa/arc/caml-list
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
Bug reports: http://caml.inria.fr/bin/caml-bugs
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