Re: [Caml-list] selecting GADT parameter

[Ashish Agarwal <agarwal1975@gmail.com>]

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Thanks for the answers. I see now the difficulty in this. (Though it seems
possible in theory if we required type annotations in various places.)

On Tue, Aug 4, 2015 at 5:21 AM, Goswin von Brederlow <goswin-v-b@web.de>
wrote:

> On Fri, Jul 31, 2015 at 09:48:13AM -0400, Ashish Agarwal wrote:
> > I have:
> >
> > type _ t =
> > | Foo1 : 'a * int -> int t
> > | Foo2 : 'a * string -> 'a t
> >
> > but I really want to merge these two cases. I want the return type to be
> > based on the second arg when the second arg is int, and be based on the
> > first arg otherwise. Any way to accomplish that?
>
> Say you had (imaginary syntax):
>
> type _ t =
> | Foo : 'a * int -> int t
> | Foo : 'a * string -> 'a t
>
> let x1 = Foo (1, 1)     : int t
> let x2 = Foo (1, "x")   : int t
>
> match (x : int t) with
> | Foo (a, b) -> ...
>
> What is the type of (a, b) now? Is it (int, int) or (int, string)?
>
> MfG
>         Goswin
>
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