Re: [Caml-list] selecting GADT parameter

[Goswin von Brederlow <goswin-v-b@web.de>]

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