[Bese-devel] Bug in UCW Examples: Add some numbers?

[Marco Baringer]

"P. Joe Bootvong" <joe13x at hotmail.com> writes:

> Expected Result:
> There are two sensible behavior I can think of:
>
> 1.) UCW think I go back to edit the last value I have entered. So It
>   should prompt me for another value. In addition to enter 10, then
>   back to edit to 5, I should be asked for one more number.

this is what should happen.

the problem is this (in ucw/examples/sum.lisp):

 (loop
   repeat how-many
   sum (call 'read-a-number) into total
   finally (call 'info-message :message (format nil "The sum is: ~D." total)))

the repeat clause of loop does not play well with
continuations. basically repeat setups a local counter and medifies
that value each time through the loop. however since this is a
modification and not a fresh binding calling the contiunation does not
undo the modification (this is the way things should be (though i
damit that it looks wrong in this particular case)).

the only way to fix is to use recursion (which gets 'undone' when
stepping back to a previous continuation):

(defaction start ((s sum))
  (let ((how-many (call 'read-a-number
                        :label "How many numbers should we read?")))
    (labels ((sum-numbers (how-many sum)
                (if (zerop how-many)
                    ;; all done
                    (call 'info-message
                          :message (format nil "The sum is: ~D." sum))
                    ;; more to go
                    (sum-numbers (1- how-many)
                                 (+ sum (call 'read-a-number))))))
      (sum-numbers how-many 0))))

NB: while writing this fix i discovered a bug in cc interpreter, local
function application was broken. UPDATE ARNESI.

> 2.) UCW think there is nothing in the page indicating that the value I
>   went back and submit is first value. So it took the new value as the
>   second number and add both result in, And return the result of 15.
>
> The current behavior is neither of this.

nope :(

-- 
-Marco
Ring the bells that still can ring.
Forget the perfect offering.
There is a crack in everything.
That's how the light gets in.
	-Leonard Cohen