Re: [Caml-list] selecting GADT parameter

[Lukasz Stafiniak <lukstafi@gmail.com>]

On the face of it, this is not possible. There must be as many pattern
matching branches as there are reachable conditions in the formulation
of the type, because only a pattern matching branch introduces a
conditional (an implication) into reasoning about types. In
particular, you need to pattern match against Tag1 and Tag2 if you
don't want to treat the parameter of the type "t" as an abstract type.

On Fri, Jul 31, 2015 at 4:18 PM, Ashish Agarwal <agarwal1975@gmail.com> wrote:
> You essentially still have 2 constructors, so this isn't quite what I'm
> aiming for.
>
>
> On Fri, Jul 31, 2015 at 9:57 AM, Carl Eastlund <ceastlund@janestreet.com>
> wrote:
>>
>> Perhaps like this?  (Caveat: I typed this straight into gmail, I haven't
>> tried to compile or run this code at all.)
>>
>> type ('a, 'b, 'c) tag =
>> | Tag1 : ('a, int, int) tag
>> | Tag2 : ('a, string, 'a) tag
>>
>> type 'a t =
>> | Foo : ('a, 'b, 'c) tag * 'a * 'b -> 'c t