Constant terms in macro parameters...

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Constant terms in macro parameters...

Postby starfleet » Wed Apr 12, 2017 11:50 am

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)
            (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...
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Re: Constant terms in macro parameters...

Postby sylwester » Wed Apr 12, 2017 5:44 pm

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.
I'm the author of two useless languages that uses BF as target machine.
Currently I'm planning a Scheme compiler :p
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Joined: Mon Jul 11, 2011 2:53 pm

Re: Constant terms in macro parameters...

Postby David Mullen » Sat Apr 15, 2017 11:59 am

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:

Code: Select all
(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-expression 1)
             (perform-expression 2)))
David Mullen
Posts: 57
Joined: Mon Dec 01, 2014 12:29 pm

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