What's wrong with my code?

What's wrong with my code?

[amal.alphonse]

Sorry if I'm posting in the wrong forum.

I have a generic package, with specification:

generic
   type Element is private;
   with procedure Element_Put(E : in Element);
package SelectionP is
   type My_Array is array (0..10) of Element;
   Max : constant Integer := 10;
   procedure Find_Min (A : My_Array; Offset : Integer; Pos : Integer);
   procedure Swap (A : in out My_Array; First : Integer; Second :
Integer);
   procedure Sort (A : in out My_Array);
   procedure Print (A : in My_Array);
end SelectionP;
--------------------------------------------------
and its package body is:

package body SelectionP is

   A : My_Array;

   procedure Find_Min (A : My_Array; Offset : Integer; Pos : Integer)
is
    ...
   end Find_Min;

   procedure Swap (A : in out My_Array; First : Integer; Second :
Integer)  is
      ...
   end Swap;

   procedure Sort (A : in out My_Array) is
     ...
   end Sort;
   procedure Print (A: in out My_Array) is
     ...
   end Print;

end SelectionP;
-------------------------------------------

And I try to make use of this package in this file:
with Ada.Text_IO, Ada.Integer_Text_IO;
with SelectionP;
procedure SelectionPUser is
   package IntSelectionP is new SelectionP(Integer, Ada.Text_IO.Put);
begin
   Ada.Text_IO.New_Line;
end SelectionPUser;

---

I try to compile but it says 'no visible subprogram matches the
specification for Element_Put' referring to the line above where I
make the new package IntSelectionP. I can't see what i've done wrong.

Also, is my code correct if my purpose is to use the package to create
arrays of different elements (integer, character, etc) and use the
procedures Find_Min and Sort and Print on them?

Thanks

Re: What's wrong with my code?

[stefan-lucks]

On Mon, 28 Apr 2008, amal.alphonse@gmail.com wrote:

> Sorry if I'm posting in the wrong forum.

You are perfectly right here. 

> with Ada.Text_IO, Ada.Integer_Text_IO;
> with SelectionP;
> procedure SelectionPUser is

Replace the following line

>    package IntSelectionP is new SelectionP(Integer, Ada.Text_IO.Put);

by

   procedure Put_Int(I: Integer) is
   begin
      Ada.Integer_Text_IO.Put(I);
   end Put_Int;

   package Int_SelectionP is new X(Integer, Put_Int);

The specification of Put in Ada.Integer_Text_IO is 
   
         procedure Put(Item  : in Num;	
                       Width : in Field := Default_Width;
                       Base  : in Number_Base := Default_Base);

Thanks to the default parameters, you can just write 
"Ada.Integer_Text_IO.Put(I);" to *call* this procedure Put. But using the 
same Put as a generic parameter appears to be different ...

> begin
>    Ada.Text_IO.New_Line;
> end SelectionPUser;

>    procedure Print (A: in out My_Array) is

Nitpick: this should be 
     procedure Print(A in My_Array) is 
to conform with the specification. 

Additional point: Most Ada programmers depreciate identifiers like 
IntSelectionP, SelectionP, ... but prefer to use underscores: 
Int_Selection_P, Selection_P. This improves readability and copes well 
with the case-insensitivity of Ada identifiers. (E.g., for ada Selections 
and SelectionS are the same, but Selections and Selection_S are different. 
I currently can't find a better example, but I hope you get the idea.)

> Also, is my code correct if my purpose is to use the package to create
> arrays of different elements (integer, character, etc) and use the
> procedures Find_Min and Sort and Print on them?

I guess you are going to compare your elements? Then you'll want to 
specify another generic parameter (in addition to the type Element and the 
procedure Element_Put), such as

  function "<"(Left, Right: Element) return Boolean;





-- 
------ Stefan Lucks   --  Bauhaus-University Weimar  --   Germany  ------
               Stefan dot Lucks at uni minus weimar dot de
------  I  love  the  taste  of  Cryptanalysis  in  the  morning!  ------

Re: What's wrong with my code?

[stefan-lucks]

> Additional point: Most Ada programmers depreciate identifiers like 
> IntSelectionP, SelectionP, ... but prefer to use underscores: 
> Int_Selection_P, Selection_P. This improves readability and copes well 
> with the case-insensitivity of Ada identifiers. (E.g., for ada Selections 
> and SelectionS are the same, but Selections and Selection_S are different. 
> I currently can't find a better example, but I hope you get the idea.)

Perhaps a better example: IntSelectionP and IntsElectionP are the same 
identifyer, but Ints_Election_P is different. 


-- 
------ Stefan Lucks   --  Bauhaus-University Weimar  --   Germany  ------
               Stefan dot Lucks at uni minus weimar dot de
------  I  love  the  taste  of  Cryptanalysis  in  the  morning!  ------

Re: What's wrong with my code?

[george.priv]

On Apr 28, 10:42 am, amal.alpho...@gmail.com wrote:
> Sorry if I'm posting in the wrong forum.
>
> I have a generic package, with specification:
>
> generic
>    type Element is private;
>    with procedure Element_Put(E : in Element);
> package SelectionP is
>    type My_Array is array (0..10) of Element;
>    Max : constant Integer := 10;
>    procedure Find_Min (A : My_Array; Offset : Integer; Pos : Integer);
>    procedure Swap (A : in out My_Array; First : Integer; Second :
> Integer);
>    procedure Sort (A : in out My_Array);
>    procedure Print (A : in My_Array);
> end SelectionP;
> --------------------------------------------------
> and its package body is:
>
> package body SelectionP is
>
>    A : My_Array;
>
>    procedure Find_Min (A : My_Array; Offset : Integer; Pos : Integer)
> is
>     ...
>    end Find_Min;
>
>    procedure Swap (A : in out My_Array; First : Integer; Second :
> Integer)  is
>       ...
>    end Swap;
>
>    procedure Sort (A : in out My_Array) is
>      ...
>    end Sort;
>    procedure Print (A: in out My_Array) is
>      ...
>    end Print;
>
> end SelectionP;
> -------------------------------------------
>
> And I try to make use of this package in this file:
> with Ada.Text_IO, Ada.Integer_Text_IO;
> with SelectionP;
> procedure SelectionPUser is
>    package IntSelectionP is new SelectionP(Integer, Ada.Text_IO.Put);

should be:

package IntSelectionP is new SelectionP(Integer,
Ada.Integer_Text_IO.Put);

> begin
>    Ada.Text_IO.New_Line;
> end SelectionPUser;
>
> ---
>
> I try to compile but it says 'no visible subprogram matches the
> specification for Element_Put' referring to the line above where I
> make the new package IntSelectionP. I can't see what i've done wrong.
>
> Also, is my code correct if my purpose is to use the package to create
> arrays of different elements (integer, character, etc) and use the
> procedures Find_Min and Sort and Print on them?

For these types you should be fine.  For more complex types you may
need to define "<" and "=" operators.

George.

>
> Thanks

Re: What's wrong with my code?

[stefan-lucks]

On Mon, 28 Apr 2008, stefan-lucks@see-the.signature wrote:

> Perhaps a better example: IntSelectionP and IntsElectionP are the same 
> identifyer, but Ints_Election_P is different. 
  I mean different from Int_Selection_P.

I hope I am done with the typos, now.


-- 
------ Stefan Lucks   --  Bauhaus-University Weimar  --   Germany  ------
               Stefan dot Lucks at uni minus weimar dot de
------  I  love  the  taste  of  Cryptanalysis  in  the  morning!  ------

Re: What's wrong with my code?

[Ivan Levashew]

amal.alphonse@gmail.com пишет:
> Sorry if I'm posting in the wrong forum.
IRC & pastebin

-- 
If you want to get to the top, you have to start at the bottom

Re: What's wrong with my code?

[christoph.grein]

Integer as an index is too big. Why not:

type Index is range 0..10;
subtype Index is Integer range 0..10;  -- alternatively
type My_Array is array (Index) of Element;

procedure Find_Min (A: My_Array; Offset, Pos: Index);
procedure Swap (A: in out My_Array; First, Second: Index);

etc

Re: What's wrong with my code?

[Ludovic Brenta]

Ivan Levashew wrote:
> amal.alphonse@gmail.com пишет:
> > Sorry if I'm posting in the wrong forum.
> IRC & pastebin

No, IMHO comp.lang.ada is much better as it is asynchronous and
archived.

--
Ludovic Brenta.

Re: What's wrong with my code?

[Ludovic Brenta]

> generic
>    type Element is private;
>    with procedure Element_Put(E : in Element);
> package SelectionP is

Others have explained why neither Ada.Text_IO.Put nor
Ada.Integer_Text_IO.Put are acceptable actuals for Element_Put.

Element_Put is only necessary for one subprogram (procedure Print).
Yet, all users of your package must provide an actual for Element_Put
even if they don't call Print. Similarly, Find_Min and Sort are likely
to require a function "<" to compare Elements. So I suggest:

generic
   type Element is private;
package Selection_P is
   type Index_Type is range 0 .. 10;
   type My_Array is array (Index_Type) of Element;

   generic
      with function "<" (Left, Right : in Element) return Boolean is
<>;
   procedure Find_Min (A : My_Array; Offset : in Index_Type; Pos : out
Index_Type);

   procedure Swap (A : in out My_Array; First, Second : Index_Type);

   generic
      with function "<" (Left, Right : in Element) return Boolean is
<>;
   procedure Sort (A : in out My_Array);

   generic
      with procedure Put (E : in Element) is <>;
   procedure Put (A : in My_Array);
end Selection_P;

The reason I didn't place "<" as a generic formal parameter of the
package, but rather of Find_Min and Sort, is because you might want to
find the maximum element but sort in ascending order, like this:

package S is new Selection_P (Element => Integer);
procedure Find_Max is new S.Find_Min ("<" => ">"); -- use ">" as the
actual
procedure Sort is new S.Sort; -- use the default "<", sort in
ascending order
procedure Put (J : in Integer) is
begin
   Ada.Integer_Text_IO.Put (J);
end Put;
procedure Put is new S.Put; -- use the default

HTH

--
Ludovic Brenta.

Re: What's wrong with my code?

[amal.alphonse]

On 28 Apr, 15:42, amal.alpho...@gmail.com wrote:
> Sorry if I'm posting in the wrong forum.
>
...
> Thanks

Thanks for the posts. I will amend my program to work. Also, I don't
need to define a comparison operation "<," I was just trying to make a
simple selection sort.

Thanks again for the help!