[Caml-list] Declaring a parameterized type in a .mli

[Caml-list] Declaring a parameterized type in a .mli

[William Smith]

Hi

I'm trying to create a generic ID module so that it is easy to make 
multiple distinct ID classes.   I want to be able to create sets and 
maps of them so I've made my signature compatible with Set.Make but I'm 
not making it that far yet.  I want to have one class of IDs for NFA 
states and another for DFA states etc. and I want to reuse the code when 
I find I need other ID classes.

Here's what I've got in my .mli:

module IDRoot :
sig
end

module GenericID ( Root : sig end ) :
sig
     type t
     val compare : t -> t -> int
     val to_string : t -> string
     val cons : unit -> t
end

module Id = GenericID( IDRoot )

I get a syntax error even though I think I am following the reference 
books online.  The error is on the equal sign of the last line:

File "broken.mli", line 13, characters 10-11:
Error: Syntax error

(For each class of IDs I will declare another IDRoot but with a 
different name.)   Is there a better way?  This one seems really simple 
if I could correct the syntax error.

Thanks for any help you can offer.

Bill Smith

Re: [Caml-list] Declaring a parameterized type in a .mli

[Ivan Gotovchits]

William Smith <bills@emu-bark.com> writes:


> module Id = GenericID( IDRoot )
Compiler is right =) You can't do this in a module type specification. 

Though you can define a signature of your module in some *.ml file and
use it later in your module type declaration.

For example:

<file sig.ml>:
   module type Id = sig
       type t
       val compare : t -> t -> int
       val to_string : t -> string
       val cons : unit -> t
   end

   module type Root = sig ... end



<file  genericId.mli>
   open Sig
   module Make(Root:Root): Id

   module DefaultId : Id
   
-- 
         (__) 
         (oo) 
   /------\/ 
  / |    ||   
 *  /\---/\ 
    ~~   ~~   
...."Have you mooed today?"...

Re: [Caml-list] Declaring a parameterized type in a .mli

[Markus Mottl]

On Sun, Apr 7, 2013 at 11:57 PM, Ivan Gotovchits <ivg@ieee.org> wrote:
> > module Id = GenericID( IDRoot )
> Compiler is right =) You can't do this in a module type specification.

Note, however, that this will work:

  module Id : module type of GenericID (IDRoot)

Regards,
Markus

Re: [Caml-list] Declaring a parameterized type in a .mli

[Ivan Gotovchits]

Markus Mottl <markus.mottl@gmail.com> writes:

> On Sun, Apr 7, 2013 at 11:57 PM, Ivan Gotovchits <ivg@ieee.org> wrote:
>> > module Id = GenericID( IDRoot )
>> Compiler is right =) You can't do this in a module type specification.
>
> Note, however, that this will work:
>
>   module Id : module type of GenericID (IDRoot)
>
> Regards,
> Markus

Absolutely... but only since 3.12.

-- 
         (__) 
         (oo) 
   /------\/ 
  / |    ||   
 *  /\---/\ 
    ~~   ~~   
...."Have you mooed today?"...