On Mar 26, 2007, at 3:17 PM, spielc wrote:
Hello everybody!
Assume i have the following function:
(deffunction my_member (?val ?list)
"implementation for member-predicate in jess"
(
(printout t (length$ (list ?list) ))
;(foreach ?element ?tail (printout t ?element))
))
I tried to call the function using Jess70p1 like this:
1. (my_member 3 (list 1 2 3 4))
Result: (my_member 3 (list 1 2 3 4))
Jess reported an error in routine call
while executing (call (printout t (length$ (list ?list))))
while executing deffunction my_member
while executing (my_member 3 (list 1 2 3 4)).
Message: Not enough arguments . <= Hmm okey what function did
ACTUALLY
fail? length$, list, printout?
The function definition is broken; there's an extra set of
parentheses around the function calls in the body. Jess interprets
this as one big function call. The return value of "(printout t
(length$ (list ?list)) crlf)" is the functor, and that "foreach" call
would be an argument if it weren't commented out. Jess sees that the
functor is a function call, so it inserts "call" as the real functor
(this is explained in the manual. Therefore you get the "(call
(printout t (length$ (list ?list))))" mentioned in the stack trace.
But "call" wants two arguments, at least: the object to call a method
on, and the name of the method. You've only supplied one argument to
"call" here, so "call" fails, and reports (as you can probably guess,
"Not enough arguments." The stack trace tells you exactly which
function failed and reported "not enough arguments", but because of
the computer-sciency name and because you didn't write it explicitly,
this wasn't obvious before; hope it is now.
There's another problem with the function, although not one you'd
notice without my pointing it out: the "list" function turns a bunch
of arguments into a list. Once a variable points to a list, it's a
list -- there's no need to call "list" again. So a proper, complete
definition would be
(deffunction my_member (?val ?list)
"implementation for member-predicate in jess"
(printout t (length$ ?list)))
(my_member 3 (list 1 2 3 4))
When fixed, this is a perfectly fine way to call the function.
---------------------------------------------------------
Ernest Friedman-Hill
Advanced Software Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
PO Box 969, MS 9012 [EMAIL PROTECTED]
Livermore, CA 94550 http://www.jessrules.com
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