gistfile1.lisp

(defun find-query (query descriptions)
  (find query descriptions
        :test (lambda (q b)
                (interpret-query q b))
        :key #'second))

(defun lookup (v bindings)
  (let ((result (assoc v bindings)))
    (if result
        (second result)
      (error "variable ~a not known" v))))

(defun interpret-query (q bindings)
  (cond ((numberp q) q)
        ((symbolp q) (lookup q bindings))
        ((consp q)
         (destructuring-bind (op a b)
             q
           (case op
             (and (and (interpret-query a bindings) (interpret-query b bindings)))
             (or  (or  (interpret-query a bindings) (interpret-query b bindings)))
             (>   (>   (interpret-query a bindings) (interpret-query b bindings)))
             (<   (<   (interpret-query a bindings) (interpret-query b bindings)))
             (=   (=   (interpret-query a bindings) (interpret-query b bindings))))))))


(defun test ()
  (find-query '(and (> length 4) (< size 8))
              '((a ((length 3) (size 5))) (b ((length 5) (size 7))))))