CLIPS: Not conditional element around class instance match

Question

I read that

CLIPS also gives you the capability of specifying an explicit not conditional element on the LHS. The absence of a fact is specified as a pattern on the LHS using the “not” conditional element.

Yet, the below code gives me a [PRNTUTIL2] Syntax Error: Check appropriate syntax for the not conditional element.

(not
    (object (is-a clips_ASDF)
        (name ?some_name)
        (property ?my_property_var))
    (test (eq ?my_property_var nil)))

This however does not cause an error:

    (object (is-a clips_ASDF)
        (name ?some_name)
        (property ?my_property_var))
    (not
        (test (eq ?my_property_var nil)))

Why is that? How can I do the first?

Answer 1

The not conditional element can only can a single conditional element. If you want to place more than one, surround them with an and conditional element:

   (not (and (object (is-a clips_ASDF)
                     (name ?some_name)
                     (property ?my_property_var))
             (test (eq ?my_property_var nil))))

Alternately, there's no need for a separate test conditional element:

   (not (object (is-a clips_ASDF)
                (name ?some_name)
                (property nil)))