(in-package :cs325-user)

(defvar *facts*
  '((bird isa animal)
    (canary isa bird)
    (penguin isa bird)
    (bird can-fly yes)
    (penguin can-fly no)
    (tweety isa canary)
    (chilly isa penguin)))

(defun matches (subj pred fact)
  (and (eql (car fact) subj)
       (eql (cadr fact) pred)))

(defun answer (subj pred facts)
  (caddr
   (find-if (lambda (fact) (matches subj pred fact))
            facts)))

(defun infer (subj pred facts)
  (or (answer subj pred facts)
      (infer (answer subj 'isa facts) pred facts)))