"<" operator

"<" operator

[dperez]

how can I write a recursive Ada Function "<" that does the less-than
comparison on linked lists of characters to do the obvious thing?


Thanks

Re: "<" operator

[Matthew Heaney]

In article <343A7434.36AD@newtimes.com>, dperez <dperez@newtimes.com> wrote:

>how can I write a recursive Ada Function "<" that does the less-than
>comparison on linked lists of characters to do the obvious thing?

function "<" 
  (L, R : Character_List) return Boolean is
begin
   if L = null then
      if R = null then
         return True;
      else
         raise <lists are not same length error>;
      end if;

   elsif R = null then
      raise <lists are not same length error>;

   else
      return L.Item < R.Item and L.Next < R.Next;

   end if;
end;


Won't that do it?

The type is

   type Character_List_Node;
   type Character_List is access Character_List_Node;

   type Character_List_Node is
      record
         Item : Character;
         Next : Character_List;
      end record;

   function "<" (L, R : Character_List) return Boolean;

--------------------------------------------------------------------
Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271

Re: "<" operator

[Mats Weber]

Assuming the guy wants lexicographic order (and wants the function to work
with lists of different lengths), I think this should be corrected as follows:

> function "<"
>   (L, R : Character_List) return Boolean is
> begin
>    if L = null then
>       if R = null then
>          return True;

should be  return False;   -- because you probably want ("" < "") = False

>       else
>          raise <lists are not same length error>;

should be  return True;    -- because "" < anything

>       end if;
> 
>    elsif R = null then
>       raise <lists are not same length error>;

should be return False;   -- because anything > ""

>    else
>       return L.Item < R.Item and L.Next < R.Next;
> 
>    end if;
> end;\x01

+ Operator

[FREBOURG Fabrice]

Hello,

I'm programming with Ada95 on Solaris 2 and I'm a beginner. I would like some information about using the "+" symbol like a pointer operator for string. 
So I've created the following example.

s: string;
.
.
.
procedure new_String(s_ptr:String_Ptr) is
begin
.
.
.
end new_String;

.
.
.
s:="hello";
new_String(+s);

Could you explain me such a mecanism because I don't understand it. Do I need
to import a special librairy. Could tell me which one.
Thank you an advance for your help.

Fabrice (frebourg@cui.unige.ch)

Re: + Operator

[Paul Chardon]

Hello Fabrice,

	Two notes about your short program. String is a unconstrained type and
therefore you can't use it to declare a variable, you must declare a
constrained type built with the string type; secondly you can use the
predefined unary "+" operator with any other type parameter.
Here is a little example that can help you.

procedure Test is

   subtype Str20 is String(1..20);

   type String_Ptr is access all Str20;

   function "+"(S : in Str20) return String_Ptr is
   begin
      return new Str20'(S);
   end "+";

   My_Str20    : Str20 := (others => ' ');   
   A_Str20_Ptr : String_Ptr;

begin
   A_Str20_Ptr:= + My_Str20 ;
end Test;

		Bye, Paul.