Re: Invade wikipedia!

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 27 Feb 2009 12:30:25 +0100, Georg Bauhaus wrote:

> Adding the declarations of suitable number types in an example
> algorithm maybe doesn't seem to hurt that much. Taking
> http://en.wikipedia.org/wiki/Insertion_sort  as an example,
> I tried
> 
>    type Mug is (Metal, Plastic, Thermo, Porcelain);
>    type Mug_Number is range 1 .. 10;
>    type Mug_List is array(Mug_Number) of Mug;
> 
>    procedure Insertion_Sort(A: in out Mug_List) is
>       j: Mug_Number'Base;
>       value: Mug;
>    begin
>       for i in A'First + 1 .. A'Last loop
>            value := A(i);
>            j := i-1;
>            while j >= A'First and then A(j) > value loop
>                 A(j+1) := A(j);
>                 j := j-1;
>            end loop;
>            A(j+1) := value;
>       end loop;
>    end Insertion_Sort;
> 
> No big changes due to going from Pseudo-Pascal to real Ada,
> I think, other than having to explain 'Base.
> The "and then" of the shifting loop actually clarifies that
> short circuit control is required.

You do not need T'Base in this case because it is cleaner and more 
efficient to rewrite it in a form that would always keep all indices within 
the array range:

   procedure Insertion_Sort (A: in out Mug_List) is
   begin
      for I in A'First + 1..A'Last loop
         declare
            Value : constant Mug := A (I);
            J     : Mug_Number   := I - 1;
         begin
            while A (J) > Value loop
               A (J + 1) := A (J);
               exit when J = A'First;
               J := J - 1;
            end loop;
            A (J) := Value;
         end;
      end loop;
   end Insertion_Sort;

Of course an Ada purist would also replace integer index arithmetic with 
I'Succ and I'Pred. But that would likely be too much for wiki brains... 
(:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de