Propositional logic example in Newlisp documentation

[jopython]

I was looking at the newlisp manual today, and this caught my eye. I want to take this example a step further.

Will it be possible to insert a function in the 'rules' database, so that i can make a query as follows?

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(query '(einstein minor))




See code below.

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(set 'facts '(
    (socrates philosopher)
    (socrates greek)
    (socrates human)
    (einstein german)
    (einstein (studied physics))
    (einstein human)
    (einstein (age 50))
))

(set 'rules '(
    ((X mortal) <- (X human))
    ((X (knows physics)) <- (X physicist))
    ((X physicist) <- (X (studied physics)))
    ((X minor)  <-   ; what should go here if i need check age is less than 18?
))


(define (query trm)
    (or  (if (find trm facts) true) (catch (prove-rule trm))))

(define (prove-rule trm)
    (dolist (r rules)
        (if (list? (set 'e (unify trm (first r))))
            (if (query (expand (last r) e))
                (throw true))))
    nil
)

#> (query '(socrates human))



[cormullion]

I know little about this, but I suspect that

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(age 50) isn't evaluated, just "matched". You might have to change the code so that there's another stage of evaluation. But perhaps Lutz can give you definitive answer....

[rickyboy]

Will it be possible to insert a function in the 'rules' database ...

Lutz talks about that in the manual.
http://www.newlisp.org/downloads/newlisp_manual.html#unify)" url="http://www.newlisp.org/downloads/newlisp_manual.html#unify%29">

Larger PROLOG implementations also allow the evaluation of terms in rules. This makes it possible to implement functions for doing other work while processing rule terms. prove-rule could accomplish this testing for the symbol eval in each rule term.