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S9 LIB (prolog list1 list2) ==> list
(new-database!) ==> unspecific
(fact! list) ==> unspecific
(predicate! list1 list2 ...) ==> unspecific
(query list) ==> list
(load-from-library "prolog.scm")
This is a tiny PROLOG interpreter that is based on an even
tinier PROLOG interpreter written in MACLISP by Ken Kahn.
The PROLOG procedures takes a query LIST1 and a database
LIST2 as arguments, attempts to prove LIST1 in LIST2, and
returns the result(s).
NEW-DATABASE! sets up a fresh PROLOG database (thereby
deleting any existing one).
FACT! adds a new fact to the database.
PREDICATE! adds a predicate with the head LIST1 and the
clauses LIST2 ... to the database.
QUERY attempts to prove LIST1. It returns a list of results.
An empty list indicates that LIST1 could not be proven.
See "prolog-test.scm" for an example program.
The following macros add some syntactic sugar for interactive
use; they allows you to write, for instance, (! (man socrates))
instead of (fact! '(man socrates)).
(! fact) ==> unspecific
(:- list1 list2 ...) ==> unspecific
(? query) ==> unspecific
The following special predicates are implemented in the
interpreter: (== A B) returns a new environment if A can be
unified with B, else NO. (Dif A B) returns NO if A can be
unified with B, else YES (use only at the end of a clause!)
(begin (! (man socrates))
(:- (mortal ?x)
(man ?x))
(query '(mortal ?who))) ==> (((who . socrates)))
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