Hi Jack,
The 'test' CE succeeds when the function call evaluates to a value
that is not the atom FALSE. I.e., other atoms, numbers, TRUE, external
addresses, etc, all succeed. Only the atom FALSE fails. This is an
excellent question, and I was surprised to find that the manual
doesn't state this specifically. It will now!
Now, the 'not' CE is entirely different. The 'not' CE doesn't work
with function calls, it works with other CEs. If you write, as you do
below,
(defrule foo1
...
(not (str-index "foo" "foo was here"))
...
(not (+ 1 1))
these patterns will succeed as long as there are no -facts- which look
like (str-index "foo" "foo was here") or (+ 1 1). I.e., these CEs have
nothing whatsoever to do with the functions str-index or + despite
appearances. The functions will never be called.
You can write (not (test (function-call))), though, and this is more
or less the same as (test (not (function-call))), but implemented
differently. In the first case, you're using the 'not' CE -- i.e.,
there's a 'not' node in the Rete network. In the second case, you're
using the 'not' function: i.e., the 'test' CE's evaluates a 'not'
function with a 'function-call' function call as an argument.
I think Jack Kerkhof wrote:
> Hi all,
>
> What is the DEFINED behavior for CE's (I.E. 'not' & 'test') when they
> are passed a non-boolean value?
>
> Context:
>
> A number of the Jess functions return EITHER a boolean or some other
> value (I.E. str-index, member$, system...)
> When these are used in a CE, what is the DEFINED behavior when the
> function return value is non-boolean?
>
> Experimentation seems to indicate that the non-boolean value is
> generally evaluated to true, but I don't really see this documented, so
> I'm not sure how to properly handle such cases.
>
> In particular, what is the RIGHT way to code function patterns with two
> possible return types?
>
> A few examples:
>
> (defrule foo1
> (test (str-index "foo" "foo was here"))
> (test (> (str-index "foo" "foo was here") 0) )
> (not (str-index "foo" "foo was here"))
> (not (str-index "goo" "foo was here"))
> =>
> (printout t "index " (str-index "foo" "foo was here") " matches
> test, test >0, not, not goo!" crlf)
> )
>
>
> (defrule foo2-contrived-eg
> (test (+ 1 1)) ; Dont' try this at home - but jess does accept it...
>
> (not (+ 1 1))
> =>
> (printout t "1+1 both tests and not!" crlf)
> )
>
> The apparent overloaded behavior of test and not can be useful in some
> contexts, but is it legitimate?
>
> Jack
>
> (ps tested in jess 5.xxx)
>
>
> ---------------------------------------------------------------------
> To unsubscribe, send the words 'unsubscribe jess-users [EMAIL PROTECTED]'
> in the BODY of a message to [EMAIL PROTECTED], NOT to the
> list (use your own address!) List problems? Notify [EMAIL PROTECTED]
> ---------------------------------------------------------------------
>
---------------------------------------------------------
Ernest Friedman-Hill
Distributed Systems Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
Org. 8920, MS 9012 [EMAIL PROTECTED]
PO Box 969 http://herzberg.ca.sandia.gov
Livermore, CA 94550
---------------------------------------------------------------------
To unsubscribe, send the words 'unsubscribe jess-users [EMAIL PROTECTED]'
in the BODY of a message to [EMAIL PROTECTED], NOT to the
list (use your own address!) List problems? Notify [EMAIL PROTECTED]
---------------------------------------------------------------------
