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From: Ole-Hjalmar Kristensen
 <ole-hjalmar.kristensen@substitute_employer_here.com>
Newsgroups: comp.lang.ada
Subject: Re: "continue/next" for "loop"
Date: 03 Nov 2003 14:54:17 +0100
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 <slrnbqckoa.m1.lutz@taranis.iks-jena.de>
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>>>>> "LD" == Lutz Donnerhacke <lutz@iks-jena.de> writes:

    LD> * amado.alves wrote:
    >>> No. I don't know how to invert a complex loop.
    >> 
    >> What on Earth are you talking about? The two constructs
    >> 
    >> (1)  if I mod J = 0 then
    >> goto next;
    >> end if;
    >> Put (I'Img);
    >> <<next>> null;
    >> 
    >> (2)  if I mod J /= 0 then
    >> Put (I'Img);
    >> end if;
    >> 
    >> are clearly equivalent!

    LD> But both are the result of an oversimplification!

    LD> outer: loop
    LD>   inner: loop
    LD>     Complex_Actions_1;
    LD>     if First_Condition then
    LD>       Some_Justify_Actions;
    LD>       goto next_outer;
    LD>     end if;
    LD>     Complex_Actions_2;
    LD>     if Second_Condition then
    LD>       Some_Other_Justify_Actions;
    LD>       goto next_outer;
    LD>     end if;
    LD>     Complex_Actions_3;
    LD>   end loop inner;
    LD>   Complex_End_Statments;
    LD>   exit outer when Other_Condition;
    LD>   More_Statments;

    LD>   <<next_outer>> null;
    LD> end loop outer;

    LD> I'd like to find a more amazing version of this braindead goto.
    LD> Please do not assume, that I'm too stupid to invert a condition in a
    LD> simplified example. IT'S NOT HOMEWORK!

It seems you are looking for a multi-level "continue" statement :-)
You need to somehow store the results of your tests if you want to
avoid the goto, because this information is used outside the scope of
the inner loop. A boolean should suffice, but is the code any more
readable?

   outer: loop
     declare 
        execute_outer_statements : boolean := false;
     begin
       inner: loop
         Complex_Actions_1;
         if First_Condition then
           Some_Justify_Actions;
         else
           Complex_Actions_2;
           if Second_Condition then
             Some_Other_Justify_Actions;
           else        
             Complex_Actions_3;
             execute_statements := true;
           end if;
         end if;
       end loop inner;
       if execute_outer_statements then
         Complex_End_Statments;
         exit outer when Other_Condition;
         More_Statments;
       end if;
     end;
   end loop outer;

You could of course make your inner loop an inline procedure returning
a boolean to separate the logic of the inner and outer loops more clearly:

   outer: loop
     declare 
       procedure inner_loop(doit : out boolean) is
       begin 
         Complex_Actions_1;
         if First_Condition then
           Some_Justify_Actions;
           doit := false;
         else
           Complex_Actions_2;
           if Second_Condition then
             Some_Other_Justify_Actions;
             doit := false;
           else        
             Complex_Actions_3;
             doit := true;
           end if;
         end if;
       end inner_loop;
       pragma inline(inner_loop);
       
       execute_outer_statements : boolean;
     begin
       inner_loop(execute_outer_statements);
       if execute_outer_statements then
         Complex_End_Statments;
         exit outer when Other_Condition;
         More_Statments;
       end if;
     end;
   end loop outer;

After looking at these alternatives, I would probably stick with the goto.

-- 
Strange attractors stole my wife