I don't think that you can currently do this.  According to the manual
entry for GADTs: "This return type must use the same type constructor as
the type being defined, and have the same number of parameters."

But I guess it would be a supportable feature to perform type substitutions
until the above is satisfied if at all possible.  Substituting manually is
probably the only thing you can do until then.

On Fri, Jun 15, 2018 at 10:35 AM Alan Schmitt <
alan.schmitt@polytechnique.org> wrote:

> Hello,
>
> I'm trying to write the following:
>
> #+begin_src ocaml
> type state
> type value
> type literal
>
> type (_,_)  term =
>   | Skip : (state, state) term
>   | Const : literal -> (state, value) term
>   | If : expr * stat * stat -> (state,state) term
> and expr = (state,value) term
> and stat = (state,state) term
> #+end_src
>
> and it works well. However I would like to replace the right-hand side
> with their abbreviations (stat and expr), and at that point the
> typechecker complains. Is there a workaround?
>
> Thanks,
>
> Alan
>
> --
> OpenPGP Key ID : 040D0A3B4ED2E5C7
> Monthly Athmospheric CO₂, Mauna Loa Obs. 2018-05: 411.25, 2017-05: 409.65
>


-- 
Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com

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