OpenEuphoria

Re: EOF and GOTO and 0th array element

• Posted by Juergen Luethje <jluethje at gmx.de> Aug 23, 2002
• 496 views

Derek <ddparnell at bigpond.com> wrote:

<snip>
>> 2. At the risk of incurring wrath for writing spaghetti code, is there a
>> GOTO equivalent?

> Yes and no. Strictly speaking there is no GOTO (thankfully).

I'm thankful for this, too.

<snip>
>> 4.  Nested in a while...end while loop is a for..end for loop.  If a
>> test fails in the for..end for loop I want to exit the while..end while
>> loop.  However, using exit command in the for..end for loop seems to
>> only exit the "for" loop and does not apply to the "while" loop.  Can
>> one indicate what to exit if using that command, or (as in the example
>> below) do I have to set some condition in the "for" loop to test outside
>> of it in order to exit the "while" loop?
>>
>> .
>> .
>> somemarker=true
>> while 1 do
>> .
>> .
>> --    test values; if fail, exit loop
>>       for y=1 to 10 do
>>            if test y fails then
>>               somemarker=false
>>               exit
>>            end if
>>       end for
>>       if somemarker=false then
>>           exit
>>       end if
>> .
>> .
>> end while
>> .
>> .
>>

> This request just keeps on coming up. Euphoria doesn't make it easy for us.
> It encourages hard-to-read code in this instance. My "pet" solution is a
> form of controlled GOTO.


>  somemarker: while 1 do
>  .
>  .
>  --    test values; if fail, exit loop
>        for y=1 to 10 do
>             if test y fails then
>                exit somemarker
>             end if
>        end for
>  .
>  .
>  end while


For handling such situations more elegant, I'd like to have an enhanced
exit-statement in Euphoria, where the numbers of levels to exit can be
given. Then this code snippet would be as simple as:

----------------------------------------
while 1 do
.
.
--    test values; if fail, exit loop
      for y=1 to 10 do
           if test y fails then
              exit 2    -- exits both the for loop and the while loop
           end if
      end for
.
.
end while
----------------------------------------

For instance, PowerBASIC has a similar feature (One has to write
"exit,exit" instead of "exit 2".) With this very simple and powerful
feature, the last argument for GOTO will disappear! 

<quote>
Many authors have suggested language features [...]
which are expressed in terms of *exit*, *jump-out*,
*break*, or *leave* statements. Kosaraju [57] has
proved that such statements are sufficient to
express all programs without *go to*'s and without
any extra computation, but only if an exit from
arbitrarily many levels of control is permitted.
<unquote>
[Knuth, Donald E.: Structured Programming with go to Statements.
 Computing Surveys, Vol. 6, No. 4, December 1974, pp. 261-301]

> ----------------
> cheers,
> Derek Parnell

Regards,
   Juergen