OpenEuphoria

Re: How can I STOP a cursed recursion?

• Posted by Juergen Luethje <j.lue at gmx.de> Jun 19, 2006
• 572 views

Dan Moyer wrote:

> Ricardo M. Forno wrote:
>
>> Hi Dan.
>> In any case, to stop a recursive procedure you must test its ending *before*
>> calling it. If not, it will recurse forever, until it eats all available
>> storage.
>> Typical example (code not tested)
>>
>> function factorial (atom x)
>>    if x = 0 then
>>       return 1
>>    end if
>>    return factorial(x - 1) * x
>> end function
> 
> Hi Ricardo,
> 
> Here's like what I did, except that I have a number of other tests inside
> the procedure which can re-call the procedue with different values to
> act on, (those tests & consequences DID work), but the STOPPING didn't work:
> 
> integer STOP
> STOP = 0
>   procedure Help()
>     if STOP then
>        return
>     end if
>     print(1,"help!")
>     Help()
>     if getTime() = 6am then
>        STOP = 1 -- How can I let the procedure *stop itself*!?
>     end if
> 
>   end procedure
>   Help()
> 
> After I get some sleep,
> I'll try Juergen's suggestion, which I think is to only call the procedure
> from within itself when some "*not*-finished" condition is met, rather than
> trying to use "return" to STOP it when the finished condition *is* met.

No, that's not the point. Previously I wrote ...

integer Count, NumTimes

procedure Help()
   puts(1,"Help!\n")
   Count += 1
   if Count < NumTimes then
      Help()
   end if
end procedure

Count = 0
NumTimes = 3
Help()

... but we can use as well:

integer Count, NumTimes

procedure Help()
   puts(1,"Help!\n")
   Count += 1
   if Count >= NumTimes then
      return
   end if
   Help()
end procedure

Count = 0
NumTimes = 3
Help()

Inspired by Ricardo's post, I see now that the same can be done without
any local (or global) variable:

procedure Help(integer times)
   if times > 0 then
      puts(1,"Help!\n")
      Help(times-1)
   end if
end procedure

Help(3)

Or ...

procedure Help(integer times)
   if times <= 0 then
      return
   end if
   puts(1,"Help!\n")
   Help(times-1)
end procedure

Help(3)

Here is an Introduction to Recursion
<http://personal.vsnl.com/erwin/recintro.htm>.

Regards,
   Juergen

-- 
Please excuse my flawed English. My native language is Euphoria.