; The code in this file was mechanically extracted from the TeX
; source files of _On Lisp_.  Some operators are multiply defined,
; as they were in the book.  Usually this means just that you get
; an upwardly compatible version 2 of whatever it is.  Note, though,
; that if you load this whole file you get:
;  1. the cltl1 versions of alrec and atrec.
;  2. varsym? defined as needed by the Prolog compiler.  So if you
;     want to use e.g. match with variables that begin with question
;     marks, comment out the final definition of varsym?

; If you have questions or comments about this code, or you want
; something I didn't include, send mail to lispcode@paulgraham.com

(proclaim '(inline last1 single append1 conc1 mklist))
(proclaim '(optimize speed))

(defun last1 (lst)
  (car (last lst)))

(defun single (lst)
  (and (consp lst) (not (cdr lst))))

(defun append1 (lst obj) 
  (append lst (list obj)))

(defun conc1 (lst obj)   
  (nconc lst (list obj)))

(defun mklist (obj)
  (if (listp obj) obj (list obj)))

(defun longer (x y)
  (labels ((compare (x y)
             (and (consp x) 
                  (or (null y)
                      (compare (cdr x) (cdr y))))))
    (if (and (listp x) (listp y))
        (compare x y)
        (> (length x) (length y)))))
 
(defun filter (fn lst)
  (let ((acc nil))
    (dolist (x lst)
      (let ((val (funcall fn x)))
        (if val (push val acc))))
    (nreverse acc)))

(defun group (source n)
  (if (zerop n) (error "zero length"))
  (labels ((rec (source acc)
             (let ((rest (nthcdr n source)))
               (if (consp rest)
                   (rec rest (cons (subseq source 0 n) acc))
                   (nreverse (cons source acc))))))
    (if source (rec source nil) nil)))

(defun flatten (x)
  (labels ((rec (x acc)
             (cond ((null x) acc)
                   ((atom x) (cons x acc))
                   (t (rec (car x) (rec (cdr x) acc))))))
    (rec x nil))) 

(defun prune (test tree)
  (labels ((rec (tree acc)
             (cond ((null tree) (nreverse acc))
                   ((consp (car tree))
                    (rec (cdr tree) 
                         (cons (rec (car tree) nil) acc)))
                   (t (rec (cdr tree)
                           (if (funcall test (car tree))
                               acc
                               (cons (car tree) acc)))))))
    (rec tree nil)))

(defun find2 (fn lst)
  (if (null lst)
      nil
      (let ((val (funcall fn (car lst))))
        (if val
            (values (car lst) val)
            (find2 fn (cdr lst))))))

(defun before (x y lst &key (test #'eql))
  (and lst
       (let ((first (car lst)))
         (cond ((funcall test y first) nil)
               ((funcall test x first) lst)
               (t (before x y (cdr lst) :test test))))))

(defun after (x y lst &key (test #'eql))
  (let ((rest (before y x lst :test test)))
    (and rest (member x rest :test test))))

(defun duplicate (obj lst &key (test #'eql))
  (member obj (cdr (member obj lst :test test)) 
          :test test))

(defun split-if (fn lst)
  (let ((acc nil))
    (do ((src lst (cdr src)))
        ((or (null src) (funcall fn (car src)))
         (values (nreverse acc) src))
      (push (car src) acc))))

(defun most (fn lst)
  (if (null lst)
      (values nil nil)
      (let* ((wins (car lst))
             (max (funcall fn wins)))
        (dolist (obj (cdr lst))
          (let ((score (funcall fn obj)))
            (when (> score max)
              (setq wins obj
                    max  score))))
        (values wins max))))

(defun best (fn lst)
  (if (null lst)
      nil
      (let ((wins (car lst)))
        (dolist (obj (cdr lst))
          (if (funcall fn obj wins)
              (setq wins obj)))
        wins)))

(defun mostn (fn lst)
  (if (null lst)
      (values nil nil)
      (let ((result (list (car lst)))
            (max (funcall fn (car lst))))
        (dolist (obj (cdr lst))
          (let ((score (funcall fn obj)))
            (cond ((> score max)
                   (setq max    score
                         result (list obj)))
                  ((= score max)
                   (push obj result)))))
        (values (nreverse result) max))))

(defun map0-n (fn n)
  (mapa-b fn 0 n))

(defun map1-n (fn n)
  (mapa-b fn 1 n))

(defun mapa-b (fn a b &optional (step 1))
  (do ((i a (+ i step))
       (result nil))
      ((> i b) (nreverse result))
    (push (funcall fn i) result)))

(defun map-> (fn start test-fn succ-fn)
  (do ((i start (funcall succ-fn i))
       (result nil))
      ((funcall test-fn i) (nreverse result))
    (push (funcall fn i) result)))

(defun mappend (fn &rest lsts)
  (apply #'append (apply #'mapcar fn lsts)))

(defun mapcars (fn &rest lsts)
  (let ((result nil))
    (dolist (lst lsts)
      (dolist (obj lst)
        (push (funcall fn obj) result)))
    (nreverse result)))

(defun rmapcar (fn &rest args)
  (if (some #'atom args)
      (apply fn args)
      (apply #'mapcar 
             #'(lambda (&rest args) 
                 (apply #'rmapcar fn args))
             args)))

(defun readlist (&rest args)
  (values (read-from-string
            (concatenate 'string "("
                                 (apply #'read-line args)
                                 ")"))))

(defun prompt (&rest args)
  (apply #'format *query-io* args)
  (read *query-io*))

(defun break-loop (fn quit &rest args)
  (format *query-io* "Entering break-loop.~%")
  (loop
    (let ((in (apply #'prompt args)))
      (if (funcall quit in)
          (return)
          (format *query-io* "~A~%" (funcall fn in))))))

(defun mkstr (&rest args)
  (with-output-to-string (s)
    (dolist (a args) (princ a s))))

(defun symb (&rest args)
  (values (intern (apply #'mkstr args))))

(defun reread (&rest args)
  (values (read-from-string (apply #'mkstr args))))

(defun explode (sym)
  (map 'list #'(lambda (c)
                 (intern (make-string 1 
                                      :initial-element c)))
             (symbol-name sym)))

(defvar *!equivs* (make-hash-table))

(defun ! (fn)
  (or (gethash fn *!equivs*) fn))

(defun def! (fn fn!)
  (setf (gethash fn *!equivs*) fn!))

(defun memoize (fn)
  (let ((cache (make-hash-table :test #'equal)))
    #'(lambda (&rest args)
        (multiple-value-bind (val win) (gethash args cache)
          (if win
              val
              (setf (gethash args cache) 
                    (apply fn args)))))))

(defun compose (&rest fns)
  (if fns
      (let ((fn1 (car (last fns)))
            (fns (butlast fns)))
        #'(lambda (&rest args)
            (reduce #'funcall fns 
                    :from-end t
                    :initial-value (apply fn1 args))))
      #'identity))

(defun fif (if then &optional else)
  #'(lambda (x)
      (if (funcall if x)
          (funcall then x)
          (if else (funcall else x)))))

(defun fint (fn &rest fns)
  (if (null fns)
      fn
      (let ((chain (apply #'fint fns)))
        #'(lambda (x) 
            (and (funcall fn x) (funcall chain x))))))

(defun fun (fn &rest fns)
  (if (null fns)
      fn
      (let ((chain (apply #'fun fns)))
        #'(lambda (x)
            (or (funcall fn x) (funcall chain x))))))

(defun lrec (rec &optional base)
  (labels ((self (lst)
             (if (null lst)
                 (if (functionp base)
                     (funcall base)
                     base)
                 (funcall rec (car lst)
                              #'(lambda () 
                                  (self (cdr lst)))))))
    #'self))

(defun rfind-if (fn tree)
  (if (atom tree)
      (and (funcall fn tree) tree)
      (or (rfind-if fn (car tree))
          (if (cdr tree) (rfind-if fn (cdr tree))))))

(defun ttrav (rec &optional (base #'identity))
  (labels ((self (tree)
             (if (atom tree)
                 (if (functionp base)
                     (funcall base tree)
                     base)
                 (funcall rec (self (car tree))
                              (if (cdr tree) 
                                  (self (cdr tree)))))))
    #'self))

(defun trec (rec &optional (base #'identity))
  (labels 
    ((self (tree)
       (if (atom tree)
           (if (functionp base)
               (funcall base tree)
               base)
           (funcall rec tree 
                        #'(lambda () 
                            (self (car tree)))
                        #'(lambda () 
                            (if (cdr tree)
                                (self (cdr tree))))))))
    #'self))

(defmacro mac (expr) 
  `(pprint (macroexpand-1 ',expr)))

(defmacro when-bind ((var expr) &body body)
  `(let ((,var ,expr))
     (when ,var
       ,@body)))

(defmacro when-bind* (binds &body body)
  (if (null binds)
      `(progn ,@body)
      `(let (,(car binds))
         (if ,(caar binds)
             (when-bind* ,(cdr binds) ,@body)))))

(defmacro with-gensyms (syms &body body)
  `(let ,(mapcar #'(lambda (s)
                     `(,s (gensym)))
                 syms)
     ,@body))

(defmacro condlet (clauses &body body)
  (let ((bodfn (gensym))
        (vars (mapcar #'(lambda (v) (cons v (gensym)))
                      (remove-duplicates
                        (mapcar #'car 
                                (mappend #'cdr clauses))))))
    `(labels ((,bodfn ,(mapcar #'car vars)
                 ,@body))
       (cond ,@(mapcar #'(lambda (cl)
                           (condlet-clause vars cl bodfn))
                       clauses)))))

(defun condlet-clause (vars cl bodfn)
  `(,(car cl) (let ,(mapcar #'cdr vars)
                (let ,(condlet-binds vars cl)
                  (,bodfn ,@(mapcar #'cdr vars))))))


(defun condlet-binds (vars cl)
  (mapcar #'(lambda (bindform)
              (if (consp bindform)
                  (cons (cdr (assoc (car bindform) vars))
                        (cdr bindform))))
          (cdr cl)))

(defmacro if3 (test t-case nil-case ?-case)
  `(case ,test
     ((nil) ,nil-case)
     (?     ,?-case)
     (t     ,t-case)))

(defmacro nif (expr pos zero neg)
  (let ((g (gensym)))
    `(let ((,g ,expr))
       (cond ((plusp ,g) ,pos)
             ((zerop ,g) ,zero)
             (t ,neg)))))

(defmacro in (obj &rest choices)
  (let ((insym (gensym)))
    `(let ((,insym ,obj))
       (or ,@(mapcar #'(lambda (c) `(eql ,insym ,c))
                     choices)))))

(defmacro inq (obj &rest args)
  `(in ,obj ,@(mapcar #'(lambda (a)
                          `',a)
                      args)))

(defmacro in-if (fn &rest choices)
  (let ((fnsym (gensym)))
    `(let ((,fnsym ,fn))
       (or ,@(mapcar #'(lambda (c)
                         `(funcall ,fnsym ,c))
                     choices)))))

(defmacro >case (expr &rest clauses)
  (let ((g (gensym)))
    `(let ((,g ,expr))
       (cond ,@(mapcar #'(lambda (cl) (>casex g cl))
                       clauses)))))

(defun >casex (g cl)
  (let ((key (car cl)) (rest (cdr cl)))
    (cond ((consp key) `((in ,g ,@key) ,@rest))
          ((inq key t otherwise) `(t ,@rest))
          (t (error "bad >case clause")))))

(defmacro while (test &body body)
  `(do ()
       ((not ,test))
     ,@body))

(defmacro till (test &body body)
  `(do ()
       (,test)
     ,@body))

(defmacro for ((var start stop) &body body)
  (let ((gstop (gensym)))
    `(do ((,var ,start (1+ ,var))
          (,gstop ,stop))
         ((> ,var ,gstop))
       ,@body)))

(defmacro do-tuples/o (parms source &body body)
  (if parms
      (let ((src (gensym)))
        `(prog ((,src ,source))
           (mapc #'(lambda ,parms ,@body)
                 ,@(map0-n #'(lambda (n)
                               `(nthcdr ,n ,src))
                           (1- (length parms))))))))

(defmacro do-tuples/c (parms source &body body)
  (if parms
      (with-gensyms (src rest bodfn)
        (let ((len (length parms)))
          `(let ((,src ,source))
             (when (nthcdr ,(1- len) ,src)
               (labels ((,bodfn ,parms ,@body))
                 (do ((,rest ,src (cdr ,rest)))
                     ((not (nthcdr ,(1- len) ,rest))
                      ,@(mapcar #'(lambda (args)
                                    `(,bodfn ,@args))
                                (dt-args len rest src))
                      nil)
                   (,bodfn ,@(map1-n #'(lambda (n)
                                         `(nth ,(1- n) 
                                               ,rest))
                                     len))))))))))
 
(defun dt-args (len rest src)
  (map0-n #'(lambda (m)
              (map1-n #'(lambda (n) 
                          (let ((x (+ m n)))
                            (if (>= x len)
                                `(nth ,(- x len) ,src)
                                `(nth ,(1- x) ,rest))))
                      len))
          (- len 2)))

(defmacro mvdo* (parm-cl test-cl &body body)
  (mvdo-gen parm-cl parm-cl test-cl body))

(defun mvdo-gen (binds rebinds test body)
  (if (null binds)
      (let ((label (gensym)))
        `(prog nil
           ,label
           (if ,(car test)
               (return (progn ,@(cdr test))))
           ,@body
           ,@(mvdo-rebind-gen rebinds)
           (go ,label)))
      (let ((rec (mvdo-gen (cdr binds) rebinds test body)))
        (let ((var/s (caar binds)) (expr (cadar binds)))
          (if (atom var/s)
              `(let ((,var/s ,expr)) ,rec)
              `(multiple-value-bind ,var/s ,expr ,rec))))))

(defun mvdo-rebind-gen (rebinds)
  (cond ((null rebinds) nil)
        ((< (length (car rebinds)) 3)
         (mvdo-rebind-gen (cdr rebinds)))
        (t
         (cons (list (if (atom (caar rebinds))
                         'setq
                         'multiple-value-setq)
                     (caar rebinds)
                     (third (car rebinds)))
               (mvdo-rebind-gen (cdr rebinds))))))

(defmacro mvpsetq (&rest args)
  (let* ((pairs (group args 2))
         (syms  (mapcar #'(lambda (p)
                            (mapcar #'(lambda (x) (gensym))
                                    (mklist (car p))))
                        pairs)))
    (labels ((rec (ps ss)
               (if (null ps)
                   `(setq
                     ,@(mapcan #'(lambda (p s)
                                   (shuffle (mklist (car p)) 
                                            s))
                               pairs syms))
                   (let ((body (rec (cdr ps) (cdr ss))))
                     (let ((var/s (caar ps))
                           (expr (cadar ps)))
                       (if (consp var/s)
                           `(multiple-value-bind ,(car ss) 
                                                 ,expr
                              ,body)
                           `(let ((,@(car ss) ,expr))
                              ,body)))))))
      (rec pairs syms))))

(defun shuffle (x y)
  (cond ((null x) y)
        ((null y) x)
        (t (list* (car x) (car y) 
                  (shuffle (cdr x) (cdr y))))))

(defmacro mvdo (binds (test &rest result) &body body)
  (let ((label (gensym))
        (temps (mapcar #'(lambda (b)
                           (if (listp (car b))
                               (mapcar #'(lambda (x) 
                                           (gensym))
                                       (car b))
                               (gensym)))
                       binds)))
    `(let ,(mappend #'mklist temps)
       (mvpsetq ,@(mapcan #'(lambda (b var)
                              (list var (cadr b)))
                          binds
                          temps))
       (prog ,(mapcar #'(lambda (b var) (list b var))
                     (mappend #'mklist (mapcar #'car binds))
                     (mappend #'mklist temps))
         ,label 
         (if ,test
             (return (progn ,@result)))
         ,@body
         (mvpsetq ,@(mapcan #'(lambda (b)
                                (if (third b)
                                    (list (car b) 
                                          (third b))))
                            binds))
         (go ,label)))))

(defmacro allf (val &rest args)
  (with-gensyms (gval)
    `(let ((,gval ,val))
       (setf ,@(mapcan #'(lambda (a) (list a gval))
                       args)))))

(defmacro nilf (&rest args) `(allf nil ,@args))

(defmacro tf (&rest args) `(allf t ,@args))

(defmacro toggle (&rest args)
  `(progn
     ,@(mapcar #'(lambda (a) `(toggle2 ,a))
               args)))

(define-modify-macro toggle2 () not)

(define-modify-macro concf (obj) nconc)

(define-modify-macro conc1f (obj) 
  (lambda (place obj)
    (nconc place (list obj))))

(define-modify-macro concnew (obj &rest args)
  (lambda (place obj &rest args)
    (unless (apply #'member obj place args)
      (nconc place (list obj)))))

(defmacro _f (op place &rest args)
  (multiple-value-bind (vars forms var set access) 
                       (get-setf-method place)
    `(let* (,@(mapcar #'list vars forms)
            (,(car var) (,op ,access ,@args)))
       ,set)))

(defmacro pull (obj place &rest args)
  (multiple-value-bind (vars forms var set access)
                       (get-setf-method place)
    (let ((g (gensym)))
      `(let* ((,g ,obj)
              ,@(mapcar #'list vars forms)
              (,(car var) (delete ,g ,access ,@args)))
         ,set))))

(defmacro pull-if (test place &rest args) 
  (multiple-value-bind (vars forms var set access) 
                       (get-setf-method place) 
    (let ((g (gensym))) 
      `(let* ((,g ,test) 
              ,@(mapcar #'list vars forms) 
              (,(car var) (delete-if ,g ,access ,@args))) 
         ,set)))) 

(defmacro popn (n place) 
  (multiple-value-bind (vars forms var set access) 
                       (get-setf-method place) 
    (with-gensyms (gn glst)
      `(let* ((,gn ,n)
              ,@(mapcar #'list vars forms)
              (,glst ,access)
              (,(car var) (nthcdr ,gn ,glst)))
         (prog1 (subseq ,glst 0 ,gn)
                ,set)))))

(defmacro sortf (op &rest places)
  (let* ((meths (mapcar #'(lambda (p)
                            (multiple-value-list 
                              (get-setf-method p)))
                        places))
         (temps (apply #'append (mapcar #'third meths))))
    `(let* ,(mapcar #'list
                    (mapcan #'(lambda (m)
                                (append (first m) 
                                        (third m)))
                            meths)
                    (mapcan #'(lambda (m)
                                (append (second m) 
                                        (list (fifth m))))
                            meths))
       ,@(mapcon #'(lambda (rest)
                     (mapcar 
                       #'(lambda (arg)
                           `(unless (,op ,(car rest) ,arg)
                              (rotatef ,(car rest) ,arg)))
                       (cdr rest)))
                 temps)
       ,@(mapcar #'fourth meths))))

(defmacro aif (test-form then-form &optional else-form)
  `(let ((it ,test-form))
     (if it ,then-form ,else-form)))

(defmacro awhen (test-form &body body)
  `(aif ,test-form
        (progn ,@body)))

(defmacro awhile (expr &body body)
  `(do ((it ,expr ,expr))
       ((not it))
     ,@body))

(defmacro aand (&rest args)
  (cond ((null args) t)
        ((null (cdr args)) (car args))
        (t `(aif ,(car args) (aand ,@(cdr args))))))

(defmacro acond (&rest clauses)
  (if (null clauses)
      nil
      (let ((cl1 (car clauses))
            (sym (gensym)))
        `(let ((,sym ,(car cl1)))
           (if ,sym
               (let ((it ,sym)) ,@(cdr cl1))
               (acond ,@(cdr clauses)))))))

(defmacro alambda (parms &body body)
  `(labels ((self ,parms ,@body))
     #'self))

(defmacro ablock (tag &rest args)
  `(block ,tag
     ,(funcall (alambda (args)
                 (case (length args)
                   (0 nil)
                   (1 (car args))
                   (t `(let ((it ,(car args)))
                         ,(self (cdr args))))))
               args)))

(defmacro aif2 (test &optional then else)
  (let ((win (gensym)))
    `(multiple-value-bind (it ,win) ,test
       (if (or it ,win) ,then ,else))))

(defmacro awhen2 (test &body body)
  `(aif2 ,test
         (progn ,@body)))

(defmacro awhile2 (test &body body)
  (let ((flag (gensym)))
    `(let ((,flag t))
       (while ,flag
         (aif2 ,test
               (progn ,@body)
               (setq ,flag nil))))))

(defmacro acond2 (&rest clauses)
  (if (null clauses)
      nil
      (let ((cl1 (car clauses))
            (val (gensym))
            (win (gensym)))
        `(multiple-value-bind (,val ,win) ,(car cl1)
           (if (or ,val ,win)
               (let ((it ,val)) ,@(cdr cl1))
               (acond2 ,@(cdr clauses)))))))

(let ((g (gensym)))
  (defun read2 (&optional (str *standard-input*))
    (let ((val (read str nil g)))
      (unless (equal val g) (values val t)))))

(defmacro do-file (filename &body body)
  (let ((str (gensym)))
    `(with-open-file (,str ,filename)
       (awhile2 (read2 ,str)
         ,@body))))

(defmacro fn (expr) `#',(rbuild expr))
 
(defun rbuild (expr)
  (if (or (atom expr) (eq (car expr) 'lambda))
      expr
      (if (eq (car expr) 'compose)
          (build-compose (cdr expr))
          (build-call (car expr) (cdr expr)))))

(defun build-call (op fns)
  (let ((g (gensym)))
    `(lambda (,g)
       (,op ,@(mapcar #'(lambda (f)
                          `(,(rbuild f) ,g))
                      fns)))))

(defun build-compose (fns)
  (let ((g (gensym)))
    `(lambda (,g)
       ,(labels ((rec (fns)
                   (if fns
                       `(,(rbuild (car fns)) 
                         ,(rec (cdr fns)))
                       g)))
          (rec fns)))))

(defmacro alrec (rec &optional base)
  "cltl2 version"
  (let ((gfn (gensym)))
    `(lrec #'(lambda (it ,gfn) 
               (symbol-macrolet ((rec (funcall ,gfn)))
                 ,rec))
           ,base)))

(defmacro alrec (rec &optional base)
  "cltl1 version"
  (let ((gfn (gensym)))
    `(lrec #'(lambda (it ,gfn)
               (labels ((rec () (funcall ,gfn)))
                 ,rec))
           ,base)))

(defmacro on-cdrs (rec base &rest lsts)
  `(funcall (alrec ,rec #'(lambda () ,base)) ,@lsts))

(defun unions (&rest sets)
  (on-cdrs (union it rec) (car sets) (cdr sets)))

(defun intersections (&rest sets)
  (unless (some #'null sets)
    (on-cdrs (intersection it rec) (car sets) (cdr sets))))

(defun differences (set &rest outs)
  (on-cdrs (set-difference rec it) set outs))

(defun maxmin (args)
  (when args
    (on-cdrs (multiple-value-bind (mx mn) rec
               (values (max mx it) (min mn it)))
             (values (car args) (car args))
             (cdr args))))

(defmacro atrec (rec &optional (base 'it))
  "cltl2 version"
  (let ((lfn (gensym)) (rfn (gensym)))
    `(trec #'(lambda (it ,lfn ,rfn)
               (symbol-macrolet ((left (funcall ,lfn))
                                 (right (funcall ,rfn)))
                 ,rec))
           #'(lambda (it) ,base))))

(defmacro atrec (rec &optional (base 'it))
  "cltl1 version"
  (let ((lfn (gensym)) (rfn (gensym)))
    `(trec #'(lambda (it ,lfn ,rfn)
               (labels ((left () (funcall ,lfn))
                        (right () (funcall ,rfn)))
                 ,rec))
           #'(lambda (it) ,base))))

(defmacro on-trees (rec base &rest trees)
  `(funcall (atrec ,rec ,base) ,@trees))

(defconstant unforced (gensym))

(defstruct delay  forced closure)

(defmacro delay (expr)
  (let ((self (gensym)))
    `(let ((,self (make-delay :forced unforced)))
       (setf (delay-closure ,self)
             #'(lambda ()
                 (setf (delay-forced ,self) ,expr)))
       ,self)))

(defun force (x)
  (if (delay-p x)
      (if (eq (delay-forced x) unforced)
          (funcall (delay-closure x))
          (delay-forced x))
      x))

(defmacro abbrev (short long)
  `(defmacro ,short (&rest args)
     `(,',long ,@args)))

(defmacro abbrevs (&rest names)
  `(progn
     ,@(mapcar #'(lambda (pair)
                   `(abbrev ,@pair))
               (group names 2))))

(defmacro propmacro (propname)
  `(defmacro ,propname (obj)
     `(get ,obj ',',propname)))

(defmacro propmacros (&rest props)
  `(progn
     ,@(mapcar #'(lambda (p) `(propmacro ,p))
               props)))

(defmacro defanaph (name &optional calls)
   (let ((calls (or calls (pop-symbol name))))
    `(defmacro ,name (&rest args)
       (anaphex args (list ',calls)))))

(defun anaphex (args expr)
  (if args
      (let ((sym (gensym)))
        `(let* ((,sym ,(car args))
                (it ,sym))
           ,(anaphex (cdr args)
                     (append expr (list sym)))))
      expr))

(defun pop-symbol (sym)
  (intern (subseq (symbol-name sym) 1)))

(defmacro defanaph (name &optional &key calls (rule :all))
  (let* ((opname (or calls (pop-symbol name)))
         (body (case rule
                 (:all   `(anaphex1 args '(,opname)))
                 (:first `(anaphex2 ',opname args))
                 (:place `(anaphex3 ',opname args)))))
    `(defmacro ,name (&rest args)
       ,body)))

(defun anaphex1 (args call)
  (if args
      (let ((sym (gensym)))
        `(let* ((,sym ,(car args))
                (it ,sym))
           ,(anaphex1 (cdr args)
                      (append call (list sym)))))
      call))

(defun anaphex2 (op args)
  `(let ((it ,(car args))) (,op it ,@(cdr args))))

(defun anaphex3 (op args)
  `(_f (lambda (it) (,op it ,@(cdr args))) ,(car args)))

(defmacro defdelim (left right parms &body body)
  `(ddfn ,left ,right #'(lambda ,parms ,@body)))

(let ((rpar (get-macro-character #\) )))
  (defun ddfn (left right fn)
    (set-macro-character right rpar)
    (set-dispatch-macro-character #\# left
      #'(lambda (stream char1 char2)
          (apply fn 
                 (read-delimited-list right stream t))))))

(defmacro dbind (pat seq &body body)
  (let ((gseq (gensym)))
    `(let ((,gseq ,seq))
       ,(dbind-ex (destruc pat gseq #'atom) body))))

(defun destruc (pat seq &optional (atom? #'atom) (n 0))
  (if (null pat)
      nil
      (let ((rest (cond ((funcall atom? pat) pat)
                        ((eq (car pat) '&rest) (cadr pat))
                        ((eq (car pat) '&body) (cadr pat))
                        (t nil))))
       (if rest
           `((,rest (subseq ,seq ,n)))
           (let ((p (car pat))
                 (rec (destruc (cdr pat) seq atom? (1+ n))))
             (if (funcall atom? p)
                 (cons `(,p (elt ,seq ,n))
                       rec)
                 (let ((var (gensym)))
                   (cons (cons `(,var (elt ,seq ,n))
                               (destruc p var atom?))
                         rec))))))))

(defun dbind-ex (binds body)
  (if (null binds)
      `(progn ,@body)
      `(let ,(mapcar #'(lambda (b)
                         (if (consp (car b))
                             (car b)
                             b))
                     binds)
        ,(dbind-ex (mapcan #'(lambda (b)
                               (if (consp (car b))
                                   (cdr b)))
                           binds)
                   body))))

(defmacro with-matrix (pats ar &body body)
  (let ((gar (gensym)))
    `(let ((,gar ,ar))
       (let ,(let ((row -1))
               (mapcan 
                 #'(lambda (pat)
                     (incf row)
                     (setq col -1)
                     (mapcar #'(lambda (p)
                                 `(,p (aref ,gar 
                                            ,row 
                                            ,(incf col))))
                              pat))
                 pats))
         ,@body))))

(defmacro with-array (pat ar &body body)
  (let ((gar (gensym)))
    `(let ((,gar ,ar))
       (let ,(mapcar #'(lambda (p)
                         `(,(car p) (aref ,gar ,@(cdr p))))
                     pat)
         ,@body))))

(defmacro with-struct ((name . fields) struct &body body)
  (let ((gs (gensym)))
    `(let ((,gs ,struct))
       (let ,(mapcar #'(lambda (f)
                         `(,f (,(symb name f) ,gs)))
                     fields)
         ,@body))))

(defmacro with-places (pat seq &body body)
  (let ((gseq (gensym)))
    `(let ((,gseq ,seq))
       ,(wplac-ex (destruc pat gseq #'atom) body))))

(defun wplac-ex (binds body)
  (if (null binds)
      `(progn ,@body)
      `(symbol-macrolet ,(mapcar #'(lambda (b)
                                     (if (consp (car b))
                                         (car b)
                                         b))
                                 binds)
        ,(wplac-ex (mapcan #'(lambda (b)
                               (if (consp (car b))
                                   (cdr b)))
                           binds)
                   body))))

(defun match (x y &optional binds)
  (acond2
    ((or (eql x y) (eql x '_) (eql y '_)) (values binds t))
    ((binding x binds) (match it y binds))
    ((binding y binds) (match x it binds))
    ((varsym? x) (values (cons (cons x y) binds) t))
    ((varsym? y) (values (cons (cons y x) binds) t))
    ((and (consp x) (consp y) (match (car x) (car y) binds))
     (match (cdr x) (cdr y) it))
    (t (values nil nil))))

(defun varsym? (x)
  (and (symbolp x) (eq (char (symbol-name x) 0) #\?)))

(defun binding (x binds)
  (labels ((recbind (x binds)
             (aif (assoc x binds)
                  (or (recbind (cdr it) binds)
                      it))))
    (let ((b (recbind x binds)))
      (values (cdr b) b))))

(defmacro if-match (pat seq then &optional else)
  `(aif2 (match ',pat ,seq)
         (let ,(mapcar #'(lambda (v)
                           `(,v (binding ',v it)))
                       (vars-in then #'atom))
           ,then)
         ,else))

(defun vars-in (expr &optional (atom? #'atom))
  (if (funcall atom? expr)
      (if (var? expr) (list expr))
      (union (vars-in (car expr) atom?)
             (vars-in (cdr expr) atom?))))

(defun var? (x)
  (and (symbolp x) (eq (char (symbol-name x) 0) #\?)))

(defun abab (seq)
  (if-match (?x ?y ?x ?y) seq
      (values ?x ?y)
      nil))

(defmacro if-match (pat seq then &optional else)
  `(let ,(mapcar #'(lambda (v) `(,v ',(gensym)))
                 (vars-in pat #'simple?))
     (pat-match ,pat ,seq ,then ,else)))

(defmacro pat-match (pat seq then else)
  (if (simple? pat)
      (match1 `((,pat ,seq)) then else)
      (with-gensyms (gseq gelse)
        `(labels ((,gelse () ,else))
           ,(gen-match (cons (list gseq seq) 
                             (destruc pat gseq #'simple?))
                       then 
                       `(,gelse))))))

(defun simple? (x) (or (atom x) (eq (car x) 'quote)))

(defun gen-match (refs then else)
  (if (null refs)
      then
      (let ((then (gen-match (cdr refs) then else)))
        (if (simple? (caar refs))
            (match1 refs then else)
            (gen-match (car refs) then else)))))

(defun match1 (refs then else)
  (dbind ((pat expr) . rest) refs
    (cond ((gensym? pat)
           `(let ((,pat ,expr))
              (if (and (typep ,pat 'sequence)
                       ,(length-test pat rest))
                  ,then
                  ,else)))
          ((eq pat '_) then)
          ((var? pat)
           (let ((ge (gensym)))
             `(let ((,ge ,expr))
                (if (or (gensym? ,pat) (equal ,pat ,ge))
                    (let ((,pat ,ge)) ,then)
                    ,else))))
          (t `(if (equal ,pat ,expr) ,then ,else)))))

(defun gensym? (s) 
  (and (symbolp s) (not (symbol-package s))))

(defun length-test (pat rest)
  (let ((fin (caadar (last rest))))
    (if (or (consp fin) (eq fin 'elt))
        `(= (length ,pat) ,(length rest))
        `(> (length ,pat) ,(- (length rest) 2)))))

(defun make-db (&optional (size 100))
  (make-hash-table :size size))

(defvar *default-db* (make-db))

(defun clear-db (&optional (db *default-db*))
  (clrhash db))

(defmacro db-query (key &optional (db '*default-db*))
  `(gethash ,key ,db))
  
(defun db-push (key val &optional (db *default-db*))
  (push val (db-query key db)))

(defmacro fact (pred &rest args)
  `(progn (db-push ',pred ',args)
          ',args))

(defmacro with-answer (query &body body)
  (let ((binds (gensym)))
    `(dolist (,binds (interpret-query ',query))
       (let ,(mapcar #'(lambda (v)
                         `(,v (binding ',v ,binds)))
                     (vars-in query #'atom))
         ,@body))))

(defun interpret-query (expr &optional binds)
  (case (car expr)   
    (and  (interpret-and (reverse (cdr expr)) binds))
    (or   (interpret-or (cdr expr) binds))
    (not  (interpret-not (cadr expr) binds))
    (t    (lookup (car expr) (cdr expr) binds))))
 
(defun interpret-and (clauses binds)
  (if (null clauses)
      (list binds)
      (mapcan #'(lambda (b)
                  (interpret-query (car clauses) b))
              (interpret-and (cdr clauses) binds))))
 
(defun interpret-or (clauses binds)
  (mapcan #'(lambda (c)
              (interpret-query c binds))
          clauses))
 
(defun interpret-not (clause binds)
  (if (interpret-query clause binds)
      nil
      (list binds)))

(defun lookup (pred args &optional binds)
  (mapcan #'(lambda (x)
              (aif2 (match x args binds) (list it)))
          (db-query pred)))

(defmacro with-answer (query &body body)
  `(with-gensyms ,(vars-in query #'simple?)
     ,(compile-query query `(progn ,@body))))

(defun compile-query (q body)
  (case (car q)
    (and  (compile-and (cdr q) body))
    (or   (compile-or  (cdr q) body))
    (not  (compile-not (cadr q) body))
    (lisp `(if ,(cadr q) ,body))
    (t    (compile-simple q body))))

(defun compile-simple (q body)
  (let ((fact (gensym)))
    `(dolist (,fact (db-query ',(car q)))
       (pat-match ,(cdr q) ,fact ,body nil))))

(defun compile-and (clauses body)
  (if (null clauses)
      body
      (compile-query (car clauses)
                     (compile-and (cdr clauses) body))))

(defun compile-or (clauses body)
  (if (null clauses)
      nil
      (let ((gbod (gensym))
            (vars (vars-in body #'simple?)))
        `(labels ((,gbod ,vars ,body))
           ,@(mapcar #'(lambda (cl)
                         (compile-query cl `(,gbod ,@vars)))
                     clauses)))))

(defun compile-not (q body)
  (let ((tag (gensym)))
    `(if (block ,tag
           ,(compile-query q `(return-from ,tag nil))
           t)
         ,body)))

(setq *cont* #'identity)

(defmacro =lambda (parms &body body) 
  `#'(lambda (*cont* ,@parms) ,@body))

(defmacro =defun (name parms &body body)
  (let ((f (intern (concatenate 'string
                                "=" (symbol-name name)))))
    `(progn
       (defmacro ,name ,parms
         `(,',f *cont* ,,@parms))
       (defun ,f (*cont* ,@parms) ,@body))))
 
(defmacro =bind (parms expr &body body)
  `(let ((*cont* #'(lambda ,parms ,@body))) ,expr))
    
(defmacro =values (&rest retvals)
  `(funcall *cont* ,@retvals))

(defmacro =funcall (fn &rest args)
  `(funcall ,fn *cont* ,@args))

(defmacro =apply (fn &rest args)
  `(apply ,fn *cont* ,@args))

(defparameter *paths* nil)
(defconstant failsym '@)

(defmacro choose (&rest choices)
  (if choices
      `(progn
         ,@(mapcar #'(lambda (c)
                       `(push #'(lambda () ,c) *paths*))
                   (reverse (cdr choices)))
         ,(car choices))
      '(fail)))

(defmacro choose-bind (var choices &body body)
  `(cb #'(lambda (,var) ,@body) ,choices))
 
(defun cb (fn choices)
  (if choices
     (progn
       (if (cdr choices)
           (push #'(lambda () (cb fn (cdr choices)))
                 *paths*))
       (funcall fn (car choices)))
     (fail)))
 
(defun fail ()
  (if *paths*
      (funcall (pop *paths*))
      failsym))

(defstruct proc  pri state wait) 

(proclaim '(special *procs* *proc*))

(defvar *halt* (gensym))

(defvar *default-proc*
        (make-proc :state #'(lambda (x) 
                              (format t "~%>> ")
                              (princ (eval (read)))
                              (pick-process))))
        
(defmacro fork (expr pri)
  `(prog1 ',expr
          (push (make-proc 
                  :state #'(lambda (,(gensym))
                             ,expr
                             (pick-process))
                  :pri   ,pri)
                *procs*)))

(defmacro program (name args &body body)
  `(=defun ,name ,args
     (setq *procs* nil)
     ,@body 
     (catch *halt* (loop (pick-process)))))

(defun pick-process ()
  (multiple-value-bind (p val) (most-urgent-process)
    (setq *proc*  p
          *procs* (delete p *procs*))
    (funcall (proc-state p) val)))
    
(defun most-urgent-process ()
  (let ((proc1 *default-proc*) (max -1) (val1 t))
    (dolist (p *procs*)
      (let ((pri (proc-pri p)))
        (if (> pri max)
            (let ((val (or (not (proc-wait p))
                           (funcall (proc-wait p)))))
              (when val
                (setq proc1 p
                      max   pri
                      val1  val))))))
    (values proc1 val1)))

(defun arbitrator (test cont)
  (setf (proc-state *proc*) cont 
        (proc-wait *proc*)  test)
  (push *proc* *procs*)
  (pick-process))
 
(defmacro wait (parm test &body body)
  `(arbitrator #'(lambda () ,test) 
               #'(lambda (,parm) ,@body))) 
 
(defmacro yield (&body body)
  `(arbitrator nil #'(lambda (,(gensym)) ,@body)))
 
(defun setpri (n) (setf (proc-pri *proc*) n))

(defun halt (&optional val) (throw *halt* val))
 
(defun kill (&optional obj &rest args)
  (if obj
      (setq *procs* (apply #'delete obj *procs* args))
      (pick-process)))

(defvar *open-doors* nil)

(=defun pedestrian () 
  (wait d (car *open-doors*)
    (format t "Entering ~A~%" d)))

(program ped () 
  (fork (pedestrian) 1))

(=defun capture (city) 
  (take city)
  (setpri 1)
  (yield
    (fortify city)))

(=defun plunder (city) 
  (loot city)
  (ransom city))

(defun take (c)    (format t "Liberating ~A.~%" c)) 
(defun fortify (c) (format t "Rebuilding ~A.~%" c)) 
(defun loot (c)    (format t "Nationalizing ~A.~%" c)) 
(defun ransom (c)  (format t "Refinancing ~A.~%" c))

(program barbarians ()   
  (fork (capture 'rome) 100)
  (fork (plunder 'rome) 98))

(defmacro defnode (name &rest arcs)
  `(=defun ,name (pos regs) (choose ,@arcs)))
 
(defmacro down (sub next &rest cmds)
  `(=bind (* pos regs) (,sub pos (cons nil regs))
     (,next pos ,(compile-cmds cmds))))
 
(defmacro cat (cat next &rest cmds)
  `(if (= (length *sent*) pos)
       (fail)
       (let ((* (nth pos *sent*)))
         (if (member ',cat (types *))
             (,next (1+ pos) ,(compile-cmds cmds))
             (fail)))))

(defmacro jump (next &rest cmds)
  `(,next pos ,(compile-cmds cmds)))

(defun compile-cmds (cmds)
  (if (null cmds)
      'regs
      `(,@(car cmds) ,(compile-cmds (cdr cmds)))))

(defmacro up (expr)
  `(let ((* (nth pos *sent*)))
     (=values ,expr pos (cdr regs))))

(defmacro getr (key &optional (regs 'regs))
  `(let ((result (cdr (assoc ',key (car ,regs)))))
     (if (cdr result) result (car result))))

(defmacro set-register (key val regs)
  `(cons (cons (cons ,key ,val) (car ,regs)) 
         (cdr ,regs)))

(defmacro setr (key val regs)
  `(set-register ',key (list ,val) ,regs))

(defmacro pushr (key val regs)
  `(set-register ',key
                 (cons ,val (cdr (assoc ',key (car ,regs))))
                 ,regs))

(defmacro with-parses (node sent &body body)
  (with-gensyms (pos regs)
    `(progn
       (setq *sent* ,sent)
       (setq *paths* nil)
       (=bind (parse ,pos ,regs) (,node 0 '(nil))
         (if (= ,pos (length *sent*))
             (progn ,@body (fail))
             (fail))))))

(defun types (word)
  (case word 
    ((do does did) '(aux v))
    ((time times) '(n v))
    ((fly flies) '(n v))
    ((like) '(v prep))
    ((liked likes) '(v))
    ((a an the) '(det))
    ((arrow arrows) '(n))
    ((i you he she him her it) '(pron))))

(defnode mods
  (cat n mods/n
    (setr mods *)))

(defnode mods/n
  (cat n mods/n
    (pushr mods *))
  (up `(n-group ,(getr mods))))

(defnode np
  (cat det np/det
    (setr det *))
  (jump np/det
    (setr det nil))
  (cat pron  pron
    (setr n *)))

(defnode pron
  (up `(np (pronoun ,(getr n)))))

(defnode np/det
  (down mods np/mods
    (setr mods *))
  (jump np/mods
    (setr mods nil)))

(defnode np/mods
  (cat n np/n
    (setr n *)))

(defnode np/n
  (up `(np (det ,(getr det))
           (modifiers ,(getr mods))
           (noun ,(getr n))))
  (down pp np/pp
    (setr pp *)))

(defnode np/pp
  (up `(np (det ,(getr det))
           (modifiers ,(getr mods))
           (noun ,(getr n))
           ,(getr pp))))

(defnode pp
  (cat prep pp/prep
    (setr prep *)))

(defnode pp/prep
  (down np pp/np
    (setr op *)))
 
(defnode pp/np
  (up `(pp (prep ,(getr prep))
           (obj ,(getr op)))))

(defnode s
  (down np s/subj
    (setr mood 'decl)
    (setr subj *))
  (cat v v
    (setr mood 'imp)
    (setr subj '(np (pron you)))
    (setr aux nil)
    (setr v *)))

(defnode s/subj
  (cat v v
    (setr aux nil)
    (setr v *)))

(defnode v
  (up `(s (mood ,(getr mood))
          (subj ,(getr subj))
          (vcl (aux ,(getr aux))
               (v ,(getr v)))))
  (down np s/obj
    (setr obj *)))

(defnode s/obj
  (up `(s (mood ,(getr mood))
          (subj ,(getr subj))
          (vcl (aux ,(getr aux))
               (v ,(getr v)))
          (obj ,(getr obj)))))

(defmacro with-inference (query &body body)
 `(progn
    (setq *paths* nil)
    (=bind (binds) (prove-query ',(rep_ query) nil)
      (let ,(mapcar #'(lambda (v) 
                        `(,v (fullbind ',v binds)))
                    (vars-in query #'atom))
        ,@body 
        (fail)))))

(defun rep_ (x)
  (if (atom x) 
      (if (eq x '_) (gensym "?") x)
      (cons (rep_ (car x)) (rep_ (cdr x)))))

(defun fullbind (x b)
  (cond ((varsym? x) (aif2 (binding x b) 
                           (fullbind it b) 
                           (gensym)))
        ((atom x) x)
        (t (cons (fullbind (car x) b) 
                 (fullbind (cdr x) b)))))

(defun varsym? (x)
  (and (symbolp x) (eq (char (symbol-name x) 0) #\?)))

(defmacro with-inference (query &rest body)
  (let ((vars (vars-in query #'simple?)) (gb (gensym)))
    `(with-gensyms ,vars
       (setq *paths* nil)
       (=bind (,gb) ,(gen-query (rep_ query))
         (let ,(mapcar #'(lambda (v) 
                           `(,v (fullbind ,v ,gb)))
                       vars)
           ,@body)
         (fail)))))

(defun varsym? (x) 
  (and (symbolp x) (not (symbol-package x))))

(defun gen-query (expr &optional binds)
  (case (car expr)
    (and (gen-and (cdr expr) binds))
    (or  (gen-or  (cdr expr) binds))
    (not (gen-not (cadr expr) binds))
    (t   `(prove (list ',(car expr) 
                       ,@(mapcar #'form (cdr expr))) 
                 ,binds))))
 
(defun gen-and (clauses binds)
  (if (null clauses)
      `(=values ,binds)
      (let ((gb (gensym)))
        `(=bind (,gb) ,(gen-query (car clauses) binds)
           ,(gen-and (cdr clauses) gb)))))
 
(defun gen-or (clauses binds)
  `(choose
     ,@(mapcar #'(lambda (c) (gen-query c binds)) 
               clauses)))
 
(defun gen-not (expr binds)
  (let ((gpaths (gensym)))
    `(let ((,gpaths *paths*))
       (setq *paths* nil)
       (choose (=bind (b) ,(gen-query expr binds)
                 (setq *paths* ,gpaths)
                 (fail))
               (progn
                 (setq *paths* ,gpaths)
                 (=values ,binds))))))

(=defun prove (query binds)
   (choose-bind r *rules* (=funcall r query binds)))

(defun form (pat)
  (if (simple? pat)
      pat
      `(cons ,(form (car pat)) ,(form (cdr pat)))))

(defvar *rules* nil)

(defmacro <- (con &rest ant)
  (let ((ant (if (= (length ant) 1) 
                 (car ant) 
                 `(and ,@ant))))
    `(length (conc1f *rules* 
                     ,(rule-fn (rep_ ant) (rep_ con))))))

(defun rule-fn (ant con)
  (with-gensyms (val win fact binds)
    `(=lambda (,fact ,binds)
       (with-gensyms ,(vars-in (list ant con) #'simple?)
         (multiple-value-bind 
             (,val ,win) 
             (match ,fact
                    (list ',(car con)
                          ,@(mapcar #'form (cdr con))) 
                    ,binds)
           (if ,win 
               ,(gen-query ant val) 
               (fail)))))))

(defun rule-fn (ant con)
  (with-gensyms (val win fact binds paths)                 ;
    `(=lambda (,fact ,binds ,paths)                        ;
       (with-gensyms ,(vars-in (list ant con) #'simple?)
         (multiple-value-bind 
             (,val ,win) 
             (match ,fact
                    (list ',(car con) 
                          ,@(mapcar #'form (cdr con))) 
                    ,binds)
           (if ,win 
               ,(gen-query ant val paths)                  ;
               (fail)))))))

(defmacro with-inference (query &rest body)
  (let ((vars (vars-in query #'simple?)) (gb (gensym)))
    `(with-gensyms ,vars
       (setq *paths* nil)
       (=bind (,gb) ,(gen-query (rep_ query) nil '*paths*) ;
         (let ,(mapcar #'(lambda (v) 
                           `(,v (fullbind ,v ,gb)))
                       vars)
           ,@body)
         (fail)))))

(defun gen-query (expr binds paths)                        ;
  (case (car expr)
    (and  (gen-and (cdr expr) binds paths))                ;
    (or   (gen-or  (cdr expr) binds paths))                ;
    (not  (gen-not (cadr expr) binds paths))               ;
    (lisp (gen-lisp (cadr expr) binds))                    ;
    (is   (gen-is (cadr expr) (third expr) binds))         ;
    (cut  `(progn (setq *paths* ,paths)                    ;
                  (=values ,binds)))                       ;
    (t    `(prove (list ',(car expr) 
                        ,@(mapcar #'form (cdr expr)))
                  ,binds *paths*))))                       ;
 
(=defun prove (query binds paths)                          ;
   (choose-bind r *rules* 
     (=funcall r query binds paths)))                      ;

(defun gen-and (clauses binds paths)                       ;
  (if (null clauses)
      `(=values ,binds)
      (let ((gb (gensym)))
       `(=bind (,gb) ,(gen-query (car clauses) binds paths);
          ,(gen-and (cdr clauses) gb paths)))))            ;

(defun gen-or (clauses binds paths)                        ;
  `(choose
     ,@(mapcar #'(lambda (c) (gen-query c binds paths))    ;
               clauses)))
 
(defun gen-not (expr binds paths)                          ;
  (let ((gpaths (gensym)))
    `(let ((,gpaths *paths*))
       (setq *paths* nil)
       (choose (=bind (b) ,(gen-query expr binds paths)    ;
                 (setq *paths* ,gpaths)
                 (fail))
               (progn
                 (setq *paths* ,gpaths)
                 (=values ,binds))))))
 
(defmacro with-binds (binds expr)
  `(let ,(mapcar #'(lambda (v) `(,v (fullbind ,v ,binds)))
                 (vars-in expr))
     ,expr))
 
(defun gen-lisp (expr binds)
  `(if (with-binds ,binds ,expr)
       (=values ,binds)
       (fail)))
 
(defun gen-is (expr1 expr2 binds)
  `(aif2 (match ,expr1 (with-binds ,binds ,expr2) ,binds)
         (=values it)
         (fail)))

(defun rget (obj prop)
  (some2 #'(lambda (a) (gethash prop a))
         (get-ancestors obj)))

(defun get-ancestors (obj)
  (labels ((getall (x)
             (append (list x)
                     (mapcan #'getall
                             (gethash 'parents x)))))
    (stable-sort (delete-duplicates (getall obj))
                 #'(lambda (x y)
                     (member y (gethash 'parents x))))))

(defun some2 (fn lst)
  (if (atom lst)
      nil
      (multiple-value-bind (val win) (funcall fn (car lst))
        (if (or val win)
            (values val win)
            (some2 fn (cdr lst))))))

(defun obj (&rest parents)
  (let ((obj (make-hash-table)))
    (setf (gethash 'parents obj) parents)
    (ancestors obj)
    obj))

(defun ancestors (obj)
  (or (gethash 'ancestors obj)
      (setf (gethash 'ancestors obj) (get-ancestors obj))))

(defun rget (obj prop)
  (some2 #'(lambda (a) (gethash prop a))
         (ancestors obj)))

(defmacro defprop (name &optional meth?)
  `(progn
     (defun ,name (obj &rest args)
       ,(if meth?
            `(run-methods obj ',name args)
            `(rget obj ',name)))
     (defsetf ,name (obj) (val)
       `(setf (gethash ',',name ,obj) ,val))))

(defun run-methods (obj name args)
  (let ((meth (rget obj name)))
    (if meth 
        (apply meth obj args)
        (error "No ~A method for ~A." name obj))))

(defstruct meth  around before primary after)

(defmacro meth- (field obj)
  (let ((gobj (gensym)))
    `(let ((,gobj ,obj))
       (and (meth-p ,gobj)
            (,(symb 'meth- field) ,gobj)))))

(defun run-methods (obj name args)
  (let ((pri (rget obj name :primary)))
    (if pri
        (let ((ar (rget obj name :around)))
          (if ar
              (apply ar obj args)
              (run-core-methods obj name args pri)))
        (error "No primary ~A method for ~A." name obj))))

(defun run-core-methods (obj name args &optional pri)
  (multiple-value-prog1
    (progn (run-befores obj name args)
           (apply (or pri (rget obj name :primary)) 
                  obj args))
    (run-afters obj name args)))

(defun rget (obj prop &optional meth (skip 0))
  (some2 #'(lambda (a) 
             (multiple-value-bind (val win) (gethash prop a)
               (if win
                   (case meth (:around  (meth- around val))
                              (:primary (meth- primary val))
                              (t (values val win))))))
         (nthcdr skip (ancestors obj))))

(defun run-befores (obj prop args)
  (dolist (a (ancestors obj))
    (let ((bm (meth- before (gethash prop a))))
      (if bm (apply bm obj args)))))

(defun run-afters (obj prop args)
  (labels ((rec (lst)
             (when lst
               (rec (cdr lst))
               (let ((am (meth- after 
                                (gethash prop (car lst)))))
                 (if am (apply am (car lst) args))))))
    (rec (ancestors obj))))

(defmacro defmeth ((name &optional (type :primary)) 
                   obj parms &body body)
  (let ((gobj (gensym)))
    `(let ((,gobj ,obj))
       (defprop ,name t)
       (unless (meth-p (gethash ',name ,gobj))
         (setf (gethash ',name ,gobj) (make-meth)))
       (setf (,(symb 'meth- type) (gethash ',name ,gobj))
             ,(build-meth name type gobj parms body)))))

(defun build-meth (name type gobj parms body)
  (let ((gargs (gensym)))
    `#'(lambda (&rest ,gargs)
          (labels 
            ((call-next ()
               ,(if (or (eq type :primary) 
                        (eq type :around))
                    `(cnm ,gobj ',name (cdr ,gargs) ,type)
                    '(error "Illegal call-next.")))
             (next-p ()
               ,(case type
                  (:around 
                   `(or (rget ,gobj ',name :around 1)
                        (rget ,gobj ',name :primary))) 
                  (:primary 
                   `(rget ,gobj ',name :primary 1))
                  (t nil))))
            (apply #'(lambda ,parms ,@body) ,gargs)))))

(defun cnm (obj name args type)
  (case type
    (:around  (let ((ar (rget obj name :around 1)))
                (if ar
                    (apply ar obj args)
                    (run-core-methods obj name args))))
    (:primary (let ((pri (rget obj name :primary 1)))
                (if pri
                    (apply pri obj args)
                    (error "No next method."))))))

(defmacro undefmeth ((name &optional (type :primary)) obj)
  `(setf (,(symb 'meth- type) (gethash ',name ,obj)) 
         nil))

(defmacro children (obj) 
  `(gethash 'children ,obj))

(defun parents (obj)
  (gethash 'parents obj))

(defun set-parents (obj pars)
  (dolist (p (parents obj))
    (setf (children p) 
          (delete obj (children p))))
  (setf (gethash 'parents obj) pars)
  (dolist (p pars)
    (pushnew obj (children p)))
  (maphier #'(lambda (obj) 
               (setf (gethash 'ancestors obj) 
                     (get-ancestors obj)))
           obj)
  pars)

(defsetf parents set-parents)

(defun maphier (fn obj)
  (funcall fn obj)
  (dolist (c (children obj))
    (maphier fn c)))

(defun obj (&rest parents)
  (let ((obj (make-hash-table)))
    (setf (parents obj) parents)
    obj))

(defmacro defcomb (name op)
  `(progn
     (defprop ,name t)
     (setf (get ',name 'mcombine)
           ,(case op
              (:standard nil)
              (:progn '#'(lambda (&rest args) 
                           (car (last args))))
              (t op)))))

(defun run-core-methods (obj name args &optional pri)
  (let ((comb (get name 'mcombine)))
    (if comb
        (if (symbolp comb)
            (funcall (case comb (:and #'comb-and)
                                (:or  #'comb-or))
                     obj name args (ancestors obj))
            (comb-normal comb obj name args))
        (multiple-value-prog1
          (progn (run-befores obj name args)
                 (apply (or pri (rget obj name :primary))
                        obj args))
          (run-afters obj name args)))))

(defun comb-normal (comb obj name args)
  (apply comb
         (mapcan #'(lambda (a)
                     (let* ((pm (meth- primary 
                                       (gethash name a)))
                            (val (if pm 
                                     (apply pm obj args))))
                        (if val (list val))))
                 (ancestors obj))))

(defun comb-and (obj name args ancs &optional (last t))
  (if (null ancs)
      last
      (let ((pm (meth- primary (gethash name (car ancs)))))
        (if pm
            (let ((new (apply pm obj args)))
              (and new 
                   (comb-and obj name args (cdr ancs) new)))
            (comb-and obj name args (cdr ancs) last)))))

(defun comb-or (obj name args ancs)
  (and ancs
       (let ((pm (meth- primary (gethash name (car ancs)))))
         (or (and pm (apply pm obj args))
             (comb-or obj name args (cdr ancs))))))

(defmacro undefmethod (name &rest args)
  (if (consp (car args))
      (udm name nil (car args))
      (udm name (list (car args)) (cadr args))))

(defun udm (name qual specs)
  (let ((classes (mapcar #'(lambda (s)
                             `(find-class ',s))
                         specs)))
    `(remove-method (symbol-function ',name)
                    (find-method (symbol-function ',name)
                                 ',qual
                                 (list ,@classes)))))

(defun compall ()
  (do-symbols (s)
    (when (fboundp s)
      (unless (compiled-function-p (symbol-function s))
        (print s)
        (compile s)))))

(defmacro check (expr)
  `(block nil
     (with-inference ,expr
       (return t))))

; This code is copyright 1993 by Paul Graham, but anyone who wants 
; to use the code in any nonprofit activity, or distribute free
; verbatim copies (including this notice), is encouraged to do so.