Merging object signatures

Merging object signatures

[Dario Teixeira]

Hi,

Similarly to polymorphic variants, is there a way for object signatures to
be merged by type name?  Consider the example at the end; I'm wondering if
it is possible for the declaration of 'foobar' to be something along the
lines of 'val foobar: int -> int -> < foo_t; bar_t >' instead of needing to
explicitly list all the methods in foo_t and bar_t.

Thanks in advance for your help!
Best regards,
Dario Teixeira


module Test:
sig
	type foo_t = < a: int >
	type bar_t = < b: int >

	val foobar: int -> int -> < a:int; b: int >

	(* val foobar: int -> int -> < foo_t; bar_t > *)
end =
struct
	type foo_t = < a: int >
	type bar_t = < b: int >

	class foo a = object method a: int = a end
	class bar b = object method b: int = b end

	let foobar a b =
	object
		inherit foo a
		inherit bar b
	end
end

Re: [Caml-list] Merging object signatures

[Goswin von Brederlow]

Dario Teixeira <darioteixeira@yahoo.com> writes:

> Hi,
>
> Similarly to polymorphic variants, is there a way for object signatures to
> be merged by type name?  Consider the example at the end; I'm wondering if
> it is possible for the declaration of 'foobar' to be something along the
> lines of 'val foobar: int -> int -> < foo_t; bar_t >' instead of needing to
> explicitly list all the methods in foo_t and bar_t.
>
> Thanks in advance for your help!
> Best regards,
> Dario Teixeira
>
>
> module Test:
> sig
> 	type foo_t = < a: int >
> 	type bar_t = < b: int >
>
> 	val foobar: int -> int -> < a:int; b: int >
>
> 	(* val foobar: int -> int -> < foo_t; bar_t > *)
> end =
> struct
> 	type foo_t = < a: int >
> 	type bar_t = < b: int >
>
> 	class foo a = object method a: int = a end
> 	class bar b = object method b: int = b end
>
> 	let foobar a b =
> 	object
> 		inherit foo a
> 		inherit bar b
> 	end
> end

Can't you make foo_t and bar_t class types and foobar_t inherits them
both?

MfG
        Goswin

Re: [Caml-list] Merging object signatures

[Dario Teixeira]

Hi,

> Can't you make foo_t and bar_t class types and foobar_t inherits them
> both?

Thanks for the reply.  Yes, in the toy example I posted that would indeed
be an alternative.  Still, I'm wondering about the most general case;
suppose I had a function that took an object satisfying both foo_t and bar_t:

val do_something: < foo_t; bar_t; .. > -> bool

This is what I'm wondering if it's possible to express.

Best regards,
Dario Teixeira

Re: [Caml-list] Merging object signatures

[Jacques Garrigue]

On 2010/11/05, at 21:58, Dario Teixeira wrote:
>> Can't you make foo_t and bar_t class types and foobar_t inherits them
>> both?
> 
> Thanks for the reply.  Yes, in the toy example I posted that would indeed
> be an alternative.  Still, I'm wondering about the most general case;
> suppose I had a function that took an object satisfying both foo_t and bar_t:
> 
> val do_something: < foo_t; bar_t; .. > -> bool
> 
> This is what I'm wondering if it's possible to express.

Same thing:

  class type foobar_t = object inherit foo_t inherit bar_t end
  val do_something : #foobar_t -> bool

I agree that this is rather verbose.
I thought a few times of adding the syntax you propose, but was always
stopped by the fact you can already do it in a verbose way.

Jacques Garrigue

Re: [Caml-list] Merging object signatures

[Dario Teixeira]

Hi,

>   class type foobar_t = object inherit foo_t inherit bar_t end
>   val do_something : #foobar_t -> bool
> 
> I agree that this is rather verbose. I thought a few times of adding the
> syntax you propose, but was always stopped by the fact you can already do
> it in a verbose way.

Actually, I was unaware that the '#' syntax could also be used for objects,
though in retrospect it does make sense given how its used with polymorphic
variants.  And verboseness notwithstanding, the code above does solve my
problem nicely -- thanks!

Best regards,
Dario Teixeira