[Caml-list] Polymorphic methods in class objects

[Caml-list] Polymorphic methods in class objects

[Narayanan Krishnamurthy]

Hi,

This is probably a very naive question,
but I'm going to ask it anyways.
I was trying to define a polymorphic
method 'foo' as shown in the class below,
but have not been able to compile it in Ocaml
because of type unification problems.
I'm not sure why this is not possible,
since the compiler should be able to build a variant type
automatically as the value of the expression 'foo'.
Is there a fundamental reason or is it because
it is against the principle of strong typing.

Other than defining variant types to deal
with this, is there any other solution?
Any help would be greatly appreciated.
Thanx.

(*********************************************)
class polym =
  object(self)
    val i = 0
    method private func1 j = j + 1
    method private func2 j = string_of_int j
    method private func3 j = float_of_int j
    method private foo polymf n = 
      polymf n
    method goo () =
      self#foo self#func1 2
    method hoo () =
      self#foo self#func2 2
    method boo () =
      self#foo self#func3 2
  end

(* I would like to do the following *)
let m = new polym

polym#goo ()  returns 3
polym#hoo ()  returns "2"
polym#boo ()  returns "2.0"

(****************************************************)
-- 
**************************************************************************
Narayanan Krishnamurthy (Nari)
ASP Advanced Tools and Methodology
Motorola SPS Architecture and Systems Platforms
Motorola Inc. Semiconductor Products Sector
7700 W. Parmer Lane, Austin, TX 78729

Loc/MD: TX32/PL30         _
email : nari@ibmoto.com /   \ email:
Narayanan.Krishnamurthy@motorola.com 
Ph    : (512) 996-4863  |O O| Fax : (512) 996-7432 
************************| I
|*********************************************
		        \ o / 
                         ---
-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners

[Caml-list] Re: Polymorphic methods in class objects

[Narayanan Krishnamurthy]

Ooops!! I'd a typo  and I've
changed it below.
Thanx.

Narayanan Krishnamurthy wrote:
> 
> Hi,
> 
> This is probably a very naive question,
> but I'm going to ask it anyways.
> I was trying to define a polymorphic
> method 'foo' as shown in the class below,
> but have not been able to compile it in Ocaml
> because of type unification problems.
> I'm not sure why this is not possible,
> since the compiler should be able to build a variant type
> automatically as the value of the expression 'foo'.
> Is there a fundamental reason or is it because
> it is against the principle of strong typing.
> 
> Other than defining variant types to deal
> with this, is there any other solution?
> Any help would be greatly appreciated.
> Thanx.
> 
> (*********************************************)
> class polym =
>   object(self)
>     val i = 0
>     method private func1 j = j + 1
>     method private func2 j = string_of_int j
>     method private func3 j = float_of_int j
>     method private foo polymf n =
>       polymf n
>     method goo () =
>       self#foo self#func1 2
>     method hoo () =
>       self#foo self#func2 2
>     method boo () =
>       self#foo self#func3 2
>   end
> 
> (* I would like to do the following *)
> let m = new polym
> 
> m#goo ()  returns 3
> m#hoo ()  returns "2"
> m#boo ()  returns "2.0"
> 
> (****************************************************)
> --
> **************************************************************************
> Narayanan Krishnamurthy (Nari)
> ASP Advanced Tools and Methodology
> Motorola SPS Architecture and Systems Platforms
> Motorola Inc. Semiconductor Products Sector
> 7700 W. Parmer Lane, Austin, TX 78729
> 
> Loc/MD: TX32/PL30         _
> email : nari@ibmoto.com /   \ email:
> Narayanan.Krishnamurthy@motorola.com
> Ph    : (512) 996-4863  |O O| Fax : (512) 996-7432
> ************************| I
> |*********************************************
>                         \ o /
>                          ---

-- 
**************************************************************************
Narayanan Krishnamurthy (Nari)
ASP Advanced Tools and Methodology
Motorola SPS Architecture and Systems Platforms
Motorola Inc. Semiconductor Products Sector
7700 W. Parmer Lane, Austin, TX 78729

Loc/MD: TX32/PL30         _
email : nari@ibmoto.com /   \ email:
Narayanan.Krishnamurthy@motorola.com 
Ph    : (512) 996-4863  |O O| Fax : (512) 996-7432 
************************| I
|*********************************************
		        \ o / 
                         ---
-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners

Re: [Caml-list] Polymorphic methods in class objects

[Brian Rogoff]

Narayanan Krishnamurthy writes:
> (*********************************************)
> class polym =
>   object(self)
>     val i = 0
>     method private func1 j = j + 1
>     method private func2 j = string_of_int j
>     method private func3 j = float_of_int j
>     method private foo polymf n = 
>       polymf n
>     method goo () =
>       self#foo self#func1 2
>     method hoo () =
>       self#foo self#func2 2
>     method boo () =
>       self#foo self#func3 2
>   end

You need a bit of explicit typing. See Section 3.10 of the manual for 
OCaml 3.06. 

# class polym =
  object(self)
    val i = 0
    method private func1 j = j + 1
    method private func2 j = string_of_int j
    method private func3 j = float_of_int j
    method private foo  : 'a . (int -> 'a) -> int -> 'a  = 
        fun polymf n -> polymf n
      method goo () =
        self#foo self#func1 2
      method hoo () =
        self#foo self#func2 2
      method boo () =
        self#foo self#func3 2
    end;;
class polym :
  object
    val i : int
    method boo : unit -> float
    method private foo : (int -> 'a) -> int -> 'a
    method private func1 : int -> int
    method private func2 : int -> string
    method private func3 : int -> float
    method goo : unit -> int
    method hoo : unit -> string
  end
# let m = new polym;;
val m : polym = <obj>
# m#goo ();;    
- : int = 3
# m#hoo ();;
- : string = "2"
# m#boo ();;              
- : float = 2.

-- Brian
-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners