OpenEuphoria

Re: Goto (Was Re: Open Source)

• Posted by Juergen Luethje <j.lue at ?mx.?e> Oct 23, 2007
• 772 views

I'm sorry for the delay in repleying.

Fernando Bauer wrote:

> Matt Lewis wrote:
> > 
> > Juergen Luethje wrote:
> > > 
> > > I do not make it a religion. Please do not put words into my mouth.
> > > I just say that it's obsolete in high-level languages. This is of
> > > course only true if a language provides sufficient other possibilities.
> > > For instance in Euphoria, it would be useful not only to have an 'exit'
> > > statement, but also the possibility to write something like
> > > 
> > >    exit <number of levels>
> > 
> > I've often thought this, too, although that construct worries me.  What
> > happens if the levels change?  Even if they don't change, it's not trivial 
> > to figure out the target of that exit.  A label-based exit, OTOH, can be 
> > very useful, and explicit.
> > 
> > For example, perl allows you to name a block (which could be a
> > while/for/etc)
> > and to use the next/last operators along with the block name:
> > 
> > <a
> > href="http://en.wikipedia.org/wiki/Perl_control_structures">http://en.wikipedia.org/wiki/Perl_control_structures</a>
> > 
> > A euphorian implementation might look like:
> > }}}
<eucode>
> > :mainloop for i = 1 to n do
> >     ...
> >     :jloop for j = 1 to m do
> >         ....
> >         if foo then 
> >             exit :mainloop 
> >         end if
> >         while foo > 5 do
> >             ...
> >             if bar then
> >                exit :jloop
> >             end if
> >             ...
> >     end for
> > end for
> > </eucode>
{{{

> > That keeps the labels firmly associated with their proper loops.

Matt, I agree that would be better than my proposal above.
BTW: I vaguely recall now, that Derek had suggested something similiar
some years ago, but I can't remember any details.

> > It 
> > makes the goal very clear, although at the expense of clarity of where
> > you're going:
> > }}}
<eucode>
> > 
> > for i = 1 to n do
> >     ...
> >     for j = 1 to m do
> >         ....
> >         if foo then 
> >             goto :mainloop 
> >         end if
> >         while foo > 5 do
> >             ...
> >             if bar then
> >                goto :jloop
> >             end if
> >             ...
> >     end for
> >     :jloop
> > end for
> > :mainloop
> > </eucode>
{{{

> > I can see benefits to both ways, though I think I would prefer keeping 
> > them associated with the loop.  It's also how exits work right now.
> > 
> > Matt
> 
> Or maybe, a more restricted solution that doesn't include labels:
>    exit <for-loop variable>
> The for-loop variable would be optional.
> 
> - Fernando

This would not always work for 'while' loops. I'd prefer a generic
solution that works for all kinds of loops.

Regards,
   Juergen