Re: GOTO considered necessary (reworked)

["John G. Volan" <johnvolan@sprintmail.com>]

Anonymous (Jeff Carter) wrote:
> 
> On 11 Jun 1997 15:40:22 -0500, smize@news.imagin.net (Samuel Mize)
> wrote:
> 
> > b) "Continue" loop logic
> >
> >    The "continue" function of C has to be emulated in Ada with a "goto":
> >
> >       loop
> >         ...
> >         goto <<CONTINUE>>
> >         ...
> >         <<CONTINUE>>
> >       end loop;
> >
> >    This is a special case of the process continuation structure.
> 
> Of course, the code in this example is the same as
> 
>    loop
>       ... -- This is the first "..." in the example
>    end loop;
> 
> since the second "..." is never executed. Real use of continue involves
> a conditional:
> 
>    loop
>       ... -- 1
> 
>       if Condition then
>          continue;
>       end if;
> 
>       ... -- 2
>    end loop;
> 
> (assuming "continue" were part of Ada :). This is equivalent to
> 
>    loop
>       ... -- 1
> 
>       if not Condition then
>          ... -- 2
>       end if;
>    end loop;
> 
> This is just as readable, and less error-prone on modification than
> using a goto.

But what if you had this:

  loop
     ... --1

     if <condition expression 1> then
       continue;
     end if;

     ... --2

     if <condition expression 2> then
       continue;
     end if;

     ... -- 3

     if <condition expression 3> then
       continue;
     end if;

     ... -- 4

  end loop;

Without goto or continue, this would have to be restructured as:

  loop
    ... --1

    if not <condition expression 1> then

      ... --2

      if not <condition expression 2> then

        ... -- 3

        if not <condition expression 3> then

          ... -- 4

        end if;
      end if;
    end if;
  end loop;

Whichever side you fall on in this debate, you have to at least agree
that a "continue" within a loop is just another example of the "process
continuation logic" situation Sam Mize described.

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