[Caml-list] Why is the parameter of a type declaration a coretype?

[Caml-list] Why is the parameter of a type declaration a coretype?

[Christoph Höger]

I am writing a syntax extension for OCaml and the following puzzles me:

and type_declaration =
    {
     ptype_name: string loc;
     ptype_params: (core_type * variance) list;
                    ^^^^^^^^^

Why is a type-parameter a core_type and not just a string? What is the
meaning of a non-variable parameter?


-- 
Christoph Höger

Technische Universität Berlin
Fakultät IV - Elektrotechnik und Informatik
Übersetzerbau und Programmiersprachen

Sekr. TEL12-2, Ernst-Reuter-Platz 7, 10587 Berlin

Tel.: +49 (30) 314-24890
E-Mail: christoph.hoeger@tu-berlin.de

Re: [Caml-list] Why is the parameter of a type declaration a coretype?

[Leo White]

It used to be a string option, but I changed it at some point. The
fundemental reason is that whilst it is syntactically an optional string
(optional because of "_"), semantically it is a core_type. For
example:

  type 'a t = T of 'b
    constraint 'a = 'b list

is essentially equivalent to (using made-up syntax):

  type 'b list t = T of 'b

This manifests as the params field in the *typed* AST being the
typed equivalent of core_type. It is slightly more convenient in
some places if the typed and untyped ASTs agree about such
things so the untyped AST uses a core type as well.

Regards,

Leo

On Mon, 26 Oct 2015, at 09:20 AM, Christoph Höger wrote:
> I am writing a syntax extension for OCaml and the following puzzles me:
> 
> and type_declaration =
>     {
>      ptype_name: string loc;
>      ptype_params: (core_type * variance) list;
>                     ^^^^^^^^^
> 
> Why is a type-parameter a core_type and not just a string? What is the
> meaning of a non-variable parameter?
> 
> 
> -- 
> Christoph Höger
> 
> Technische Universität Berlin
> Fakultät IV - Elektrotechnik und Informatik
> Übersetzerbau und Programmiersprachen
> 
> Sekr. TEL12-2, Ernst-Reuter-Platz 7, 10587 Berlin
> 
> Tel.: +49 (30) 314-24890
> E-Mail: christoph.hoeger@tu-berlin.de
> 
> -- 
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