Constant terms in macro parameters...

[starfleet]

Greetings, this is not homework, but I felt it would be here the best place to post...

I'm trying to program a common-lisp macro (sbcl) to set the syntax for defining a rule in a rule-based system.
My goal is to allow users to specify rules in a syntax like this:

Code: Select all

(defrule  "name of the rule"
    :when   (s-expression 1)
            (s-expression 2)
            ...
            (s-expression n)
    :perform
            (s-expresion 1)
            (s-expression 2)
            ...
            (s-expression m) )

And I face two problems I currently don't know how to solve:

First, is there an intelligent way to include the constant terms (:when and :perform) without adding them as specific parameters to the macro?

Second, How do I accept two chunks of unknown number of s-expressions without forcing the user to delimit all the lhs and rhs expressions in a list?

Although I have reviewed many codes with rule-based systems (CL-mycyn, Leibniz, Lisa, etc) the only problem seems to be my inexperience with macros and CL in general...
Any help will be greatly appreciated...

Thanks in advance...

[sylwester]

Code: Select all

(defmacro defrule (name &rest rest)
  ...)

Now name will be "name of the rule" and rest will be (:when (s-expression 1) ... :perform (s-expresion 1) ...)
Your macro can iterate and collect and do all sorts of things and you look for :when and :perform to switch mode.

[David Mullen]

Seems like it might be easiest—if not the right thing in your case—to just look for any keywords to delimit the associated expressions, rather than specific keywords. Sticking them in a property list makes the rule definition a bit more tractable:

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(defun rule-definition-plist (body)
  (loop with plist for (keyword . tail) = body
        until (endp body) finally (return plist)
        do (check-type keyword keyword)
           (setq body (member-if #'keywordp tail))
           (let ((key-expressions (ldiff tail body)))
             (setf (getf plist keyword) key-expressions))))

Of course, the plist will tend to be in the reverse order:

Code: Select all

? (rule-definition-plist
   '(:when   (when-expression 1)
             (when-expression 2)
     :perform
             (perform-expression 1)
             (perform-expression 2)))
(:PERFORM ((PERFORM-EXPRESSION 1) (PERFORM-EXPRESSION 2))
 :WHEN ((WHEN-EXPRESSION 1) (WHEN-EXPRESSION 2)))