Re: Hierarchical States Machines

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert I. Eachus" <rieachus@comcast.net> wrote in message
news:jrOdnQYzWKMxkQ3dRVn-hQ@comcast.com...
> Incidentally, as far as I know, or for that matter most Ada experts
> know, this is the only area in Ada where you should use gotos.  But goto
> has been kept in the language primarily because it is _necessary_ to
> create maintainable finite state machines, push-down automata, and the
like.

Ah, baloney. :-)

I use gotos whenever they prevent duplicating work that otherwise would have
to be done. It's silly to have two copies of code to do something just to
avoid a goto (or to make such code into a subprogram with no purpose other
than to avoid a goto).

A common case is to emulate the missing "continue" that Ada doesn't have. It
usually shows up in some deeply nested code:

    loop
        <bunch of conditions>
            <Do some processing>
            if <unusual condition> then
                  <Handle unusual case>
                  goto Continue;
           end if;
       <bunch of else conditions>
       end if;
       <normal processing>;
     <<continue>> null;
   end loop;

You can avoid the goto by making a hash out of the code, but why bother?
Gotos are efficient, not particularly unstructured in Ada (most of the bad
cases are illegal) - compiler optimizers are unlikely to be able to get rid
of batches of boolean flags and turn them into the branches that really were
intended in the first place.

                       Randy.