OpenEuphoria

Re: Good Use of GOTO

• Posted by Derek Parnell <ddparnell at b?gp?nd.com> Jun 06, 2008
• 840 views

Kat wrote:

> I gave code for that also. It involved:
> goto exit
> goto retry
> goto restart
> goto next
> goto cleanup&return
> etc.
> 
> The only way that's not clear is if you don't read english.

For example:

   ----- fileA.e ----
   function qwerty( integer b)
   integer a
   a = b
   label start:
   if a < 10 then
     a = foo(b)
     if a < 0 then
        goto exit  -- Which exit does this go to?
     end if
     b = bar(a)
     goto start    -- which start?
   end if
   label exit:

   label start:
   a = 5
   while a < 10 do
     a = bar(b)
     if a < 0 then
        goto exit
     end if
     b = foo(a)
     foto start
   end if
   label exit:

   return a
   end function

Oh hang on, all labels in the scope must be unique. So now I have to numbering?
them.

   function qwerty( integer b)
   integer a
   a = b
   label start:
   if a < 10 then
     a = foo(b)
     if a < 0 then
        goto exit
     end if
     b = bar(a)
     goto start
   end if
   label exit:

   label start1:
   a = 5
   if a < 10 do
     a = bar(b)
     if a < 0 then
        goto exit1
     end if
     b = foo(a)
     goto start1
   end if
   label exit1:

   return a
   end function

So now not only do I have more to type and more to read I also have to create
unique label names.

Then we've got this sort of problem....

   a = b
   label exit:
   if a < 10 then
     a = foo(b)
     if a < 0 then
        goto start
     end if
     b = bar(a)
     goto exit
   end if
   label start:

Identical syntax from Euphoria's point of view, but very misleading for humans
to read. Yes, I know is a silly example but the point is that it is possible to
use label names that are actually misleading in terms of informing the reader
about the coder's intentions.


The solution we have chosen is this ...

   function qwerty( integer b)
   integer a
   a = b

   while a < 10 do
     a = foo(b)
     if a < 0 then
        exit
     end if
     b = bar(a)
   end while

   a = 5
   while a < 10 do
     a = bar(b)
     if a < 0 then
        exit
     end if
     b = foo(a)
   end while

   return a
   end function

There is no misleading control flow statements now. They are shorter. They
inform you of the coder's intentions. And this is already in Euphoria 3.1


-- 
Derek Parnell
Melbourne, Australia
Skype name: derek.j.parnell