Re: [Caml-list] Matching exhausitvity with GADT and modules

[Yannis Juglaret <yjuglaret@gmail.com>]

Hi,

Removing this warning is not a good solution, because this warning may 
be relevant the day you update your GADT. As far as I know, you should 
always be using concrete types. Read for example: 
<http://stackoverflow.com/questions/20692885/gadt-definition>.

This is a question to the list: is there any good reason for allowing 
abstract types in module implementations, and not just in module 
signatures -- where they can actually be used to abstract types?

-- Yannis

Le 27/05/2015 17:22, Joris Giovannangeli a écrit :
>
>> This is a common problem that has annoyed me as well. The issue is that
>> B sees foo and bar as abstract types, so cannot be sure they are
>> different, so cannot be sure that a value of type foo gadt can't be
>> constructed with Bar. If you add explicit constructors for both
>> currently-empty types, then their inequality will be exposed and your
>> pattern match should work.
>
> That's a nice workaround in the case where foo and bar and phantom types
> indeed. Just adding a dummy constructor. In case they are real abstract
> type, someone advised me to disable the exhaustivity warning locally
> with [@@warning "-8"] code annotation, which is a bit more hack-ish.
>
> Thanks
>
>