OpenEuphoria

Re: GOTO

• Posted by Tony Bucholtz <tony_bucholtz at HOTMAIL.COM> Jan 21, 2001
• 475 views

G'day all

I get my postings via digest, and haven't followed this thread word for
word, so if I'm repeating someone else's ideas... oops, sorry :(

Using the following as an example:

while 1 do
   while 1 do
      if condition then
         doExit = true -- set flag
         exit
      end if
   end while
   -- we now have to check this flag "every time"
   if doExit = true then
      exit
   end if
   -- more code
end while

can lead to some ugly code (especially when the doExit flag is a long way
from the interior end while, or where lots of conditions are being tested,
etc. What I propose is a new "until" statement, in the form

   until <condition> then
      -- code
   end until

The code inside the "until" block would execute until <condition> becomes
true. Euphoria could detect that <condition> had become true at any point
in the code, and "pretend" that the programmer had coded an "if..exit..end
if" thing. For example:

until doExit = true do
   while 1 do
      if condition then
         doExit = true -- triggers immediate exit from "until" block
      end if
   end while
   -- more code (run only if doExit is still false)
end until

This change to the language would result in nice neat code, and wouldn't
break any existing stuff out there. Of course, it should be possible to
use a normal "exit" statement somewhere inside the "until" block, eg:

until doExit = true do
   while 1 do
      if condition1 then
         doExit = true -- triggers immediate exit from "until" block
      end if
      -- some more code (run only if doExit is still false)
      if condition2 then
         exit -- only exit from this "while" block
      end if
      for i = 1 to 20 do
         if condition3 then
            doExit = true -- triggers immediate exit from "until" block
         end if
         -- some more code (run only if doExit is still false)
         if condition4 then
            exit
         end if
      next
   end while
   -- more code (run only if "exit" used inside "while" loop)
end until

The "until" statement should be able to handle multiple flags by a method
similar to the next example. This example shows a method for determining
where in the "until" block the exit came from, as well as an example of
exiting a for loop:

until or_all(doExit1, doExit2) = true do
   while 1 do
      if condition1 then
         doExit1 = true -- triggers immediate exit from "until" block
      end if
      -- some more code (run only if doExit is still false)
      if condition2 then
         exit -- only exit from this "while" block
      end if
      for i = 1 to 20 do
         if condition3 then
            doExit2 = true -- triggers immediate exit from "until" block
         end if
         -- some more code (run only if doExit is still false)
         if condition4 then
            exit
         end if
      next
   end while
   -- more code (run only if "exit" used inside "while" loop)
end until
if doExit1 = true then
   -- oopscode #1
elsif doExit2 = true then
   -- oopscode #2
end if

This assumes that a "goto"-like thing would only be used for exiting loops,
and not implemented in a "goto label" style generic goto. Personally, I've
maintained enough spaghetti code already in this lifetime, and I'd hate to
see Euspaghetti!

Regards
Tony