[cl-unification-devel] simple question

5 Jun 2008

      I'm just learning how to use cl-unification.  I have written some code that doesn't work the way I expect, but of course this probably means that my expectations are wrong.

Can one of the cl-unification gurus take a look, and let me know what I'm doing wrong?

Thanks,

-russ

(defpackage :unification-demo
  (:use :cl :CL.EXT.DACF.UNIFICATION))

(in-package :unification-demo)

(declaim (optimize (debug 3) (speed 0)))

(defclass call-expr ()
  ((rator :reader rator)
   (rands :reader rands)))

(defmethod initialize-instance :after ((call-expr call-expr) &key form)
  (with-slots (rator rands) call-expr
    (destructuring-bind (rator-form &rest rand-forms) form
      (setf rator rator-form
            rands (mapcar (lambda (rand-form) (parse-expr rand-form))
                          rand-forms)))))

(defclass var-ref ()
  ((var :initarg :var :reader var)))

(defclass let-binding ()
  ((var :reader let-binding-var :initarg :var)
   (expr :reader let-binding-expr :initarg :expr)))

(defmethod initialize-instance :after ((let-binding let-binding) &key form)
  (with-slots (var expr) let-binding
    (destructuring-bind (var-form expr-form) form
      (setf var var-form
            expr (parse-expr expr-form)))))

(defclass let-expr ()
  ((bindings :reader bindings)
   (body :reader body)))

(defmethod initialize-instance :after ((let-expr let-expr) &key form)
  (with-slots (bindings body) let-expr
    (destructuring-bind (binding-forms body-form) (cdr form)
      (setf bindings (mapcar (lambda (form) (make-instance 'let-binding :form form))
                             binding-forms)
            body (parse-expr body-form)))))

(defun parse-expr (form)
  (flet ((car-match (indicator)
           (and (consp form) (eql (car form) indicator)))
         (constant-match ()
           (or (stringp form)
               (numberp form))))
    (cond ((constant-match) form)
          ((car-match 'let) (make-instance 'let-expr :form form))
          ((car-match 'lambda) (make-instance 'lambda-expr :form form))
          ((consp form) (make-instance 'call-expr :form form))
          ((symbolp form) (make-instance 'var-ref :var form))
          (t (error "unhandled form ~A" form)))))

;; this works                                                                                                                                            
(find-variable-value '?bs (unify #T(let-expr bindings ?bs)
                                 (parse-expr
                                  '(let ((x 1) (y 2))
                                    (+ x y)))))

;; this fails, why?                                                                                                                                      
(find-variable-value '?b (unify #T(let-expr bindings (list ?b &rest ?bs))
                                (parse-expr
                                 '(let ((x 1) (y 2))
                                   (+ x y)))))

Russell McManus

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