lists.lisp

   1 (in-package :alexandria)
   2
   3 (declaim (inline safe-endp))
   4 (defun safe-endp (x)
   5   (declare (optimize safety))
   6   (endp x))
   7
   8 (defun alist-plist (alist)
   9   "Returns a property list containing the same keys and values as the
  10 association list ALIST in the same order."
  11   (let (plist)
  12     (dolist (pair alist)
  13       (push (car pair) plist)
  14       (push (cdr pair) plist))
  15     (nreverse plist)))
  16
  17 (defun plist-alist (plist)
  18   "Returns an association list containing the same keys and values as the
  19 property list PLIST in the same order."
  20   (let (alist)
  21     (do ((tail plist (cddr tail)))
  22         ((safe-endp tail) (nreverse alist))
  23       (push (cons (car tail) (cadr tail)) alist))))
  24
  25 (declaim (inline racons))
  26 (defun racons (key value ralist)
  27   (acons value key ralist))
  28
  29 (macrolet
  30     ((define-alist-get (name get-entry get-value-from-entry add doc)
  31        `(progn
  32           (declaim (inline ,name))
  33           (defun ,name (alist key &key (test 'eql))
  34             ,doc
  35             (let ((entry (,get-entry key alist :test test)))
  36               (values (,get-value-from-entry entry) entry)))
  37           (define-setf-expander ,name (place key &key (test ''eql)
  38                                        &environment env)
  39             (multiple-value-bind
  40                   (temporary-variables initforms newvals setter getter)
  41                 (get-setf-expansion place env)
  42               (when (cdr newvals)
  43                 (error "~A cannot store multiple values in one place" ',name))
  44               (with-unique-names (new-value key-val test-val alist entry)
  45                 (values
  46                  (append temporary-variables
  47                          (list alist
  48                                key-val
  49                                test-val
  50                                entry))
  51                  (append initforms
  52                          (list getter
  53                                key
  54                                test
  55                                `(,',get-entry ,key-val ,alist :test ,test-val)))
  56                  `(,new-value)
  57                  `(cond
  58                     (,entry
  59                      (setf (,',get-value-from-entry ,entry) ,new-value))
  60                     (t
  61                      (let ,newvals
  62                        (setf ,(first newvals) (,',add ,key ,new-value ,alist))
  63                        ,setter
  64                        ,new-value)))
  65                  `(,',get-value-from-entry ,entry))))))))
  66  (define-alist-get assoc-value assoc cdr acons
  67 "ASSOC-VALUE is an alist accessor very much like ASSOC, but it can
  68 be used with SETF.")
  69  (define-alist-get rassoc-value rassoc car racons
  70 "RASSOC-VALUE is an alist accessor very much like RASSOC, but it can
  71 be used with SETF."))
  72
  73 (defun malformed-plist (plist)
  74   (error "Malformed plist: ~S" plist))
  75
  76 (defmacro doplist ((key val plist &optional values) &body body)
  77   "Iterates over elements of PLIST. BODY can be preceded by
  78 declarations, and is like a TAGBODY. RETURN may be used to terminate
  79 the iteration early. If RETURN is not used, returns VALUES."
  80   (multiple-value-bind (forms declarations) (parse-body body)
  81     (with-gensyms (tail loop results)
  82       `(block nil
  83          (flet ((,results ()
  84                   (let (,key ,val)
  85                     (declare (ignorable ,key ,val))
  86                     (return ,values))))
  87            (let* ((,tail ,plist)
  88                   (,key (if ,tail
  89                             (pop ,tail)
  90                             (,results)))
  91                  (,val (if ,tail
  92                            (pop ,tail)
  93                            (malformed-plist ',plist))))
  94             (declare (ignorable ,key ,val))
  95             ,@declarations
  96             (tagbody
  97                ,loop
  98                ,@forms
  99                (setf ,key (if ,tail
 100                               (pop ,tail)
 101                               (,results))
 102                      ,val (if ,tail
 103                               (pop ,tail)
 104                               (malformed-plist ',plist)))
 105                (go ,loop))))))))
 106
 107 (define-modify-macro appendf (&rest lists) append
 108   "Modify-macro for APPEND. Appends LISTS to the place designated by the first
 109 argument.")
 110
 111 (define-modify-macro nconcf (&rest lists) nconc
 112   "Modify-macro for NCONC. Concatenates LISTS to place designated by the first
 113 argument.")
 114
 115 (define-modify-macro unionf (list &rest args) union
 116   "Modify-macro for UNION. Saves the union of LIST and the contents of the
 117 place designated by the first argument to the designated place.")
 118
 119 (define-modify-macro nunionf (list &rest args) nunion
 120   "Modify-macro for NUNION. Saves the union of LIST and the contents of the
 121 place designated by the first argument to the designated place. May modify
 122 either argument.")
 123
 124 (define-modify-macro reversef () reverse
 125   "Modify-macro for REVERSE. Copies and reverses the list stored in the given
 126 place and saves back the result into the place.")
 127
 128 (define-modify-macro nreversef () nreverse
 129   "Modify-macro for NREVERSE. Reverses the list stored in the given place by
 130 destructively modifying it and saves back the result into the place.")
 131
 132 (defun circular-list (&rest elements)
 133   "Creates a circular list of ELEMENTS."
 134   (let ((cycle (copy-list elements)))
 135     (nconc cycle cycle)))
 136
 137 (defun circular-list-p (object)
 138   "Returns true if OBJECT is a circular list, NIL otherwise."
 139   (and (listp object)
 140        (do ((fast object (cddr fast))
 141             (slow (cons (car object) (cdr object)) (cdr slow)))
 142            (nil)
 143          (unless (and (consp fast) (listp (cdr fast)))
 144            (return nil))
 145          (when (eq fast slow)
 146            (return t)))))
 147
 148 (defun circular-tree-p (object)
 149   "Returns true if OBJECT is a circular tree, NIL otherwise."
 150   (labels ((circularp (object seen)
 151              (and (consp object)
 152                   (do ((fast (cons (car object) (cdr object)) (cddr fast))
 153                        (slow object (cdr slow)))
 154                       (nil)
 155                     (when (or (eq fast slow) (member slow seen))
 156                       (return-from circular-tree-p t))
 157                     (when (or (not (consp fast)) (not (consp (cdr slow))))
 158                       (return
 159                         (do ((tail object (cdr tail)))
 160                             ((not (consp tail))
 161                              nil)
 162                           (let ((elt (car tail)))
 163                             (circularp elt (cons object seen))))))))))
 164     (circularp object nil)))
 165
 166 (defun proper-list-p (object)
 167   "Returns true if OBJECT is a proper list."
 168   (cond ((not object)
 169          t)
 170         ((consp object)
 171          (do ((fast object (cddr fast))
 172               (slow (cons (car object) (cdr object)) (cdr slow)))
 173              (nil)
 174            (unless (and (listp fast) (consp (cdr fast)))
 175              (return (and (listp fast) (not (cdr fast)))))
 176            (when (eq fast slow)
 177              (return nil))))
 178         (t
 179          nil)))
 180
 181 (deftype proper-list ()
 182   "Type designator for proper lists. Implemented as a SATISFIES type, hence
 183 not recommended for performance intensive use. Main usefullness as a type
 184 designator of the expected type in a TYPE-ERROR."
 185   `(and list (satisfies proper-list-p)))
 186
 187 (defun circular-list-error (list)
 188   (error 'type-error
 189          :datum list
 190          :expected-type '(and list (not circular-list))))
 191
 192 (macrolet ((def (name lambda-list doc step declare ret1 ret2)
 193              (assert (member 'list lambda-list))
 194              `(defun ,name ,lambda-list
 195                 ,doc
 196                 (do ((last list fast)
 197                      (fast list (cddr fast))
 198                      (slow (cons (car list) (cdr list)) (cdr slow))
 199                      ,@(when step (list step)))
 200                     (nil)
 201                   (declare (dynamic-extent slow) ,@(when declare (list declare))
 202                            (ignorable last))
 203                   (when (safe-endp fast)
 204                     (return ,ret1))
 205                   (when (safe-endp (cdr fast))
 206                     (return ,ret2))
 207                   (when (eq fast slow)
 208                     (circular-list-error list))))))
 209   (def proper-list-length (list)
 210     "Returns length of LIST, signalling an error if it is not a proper list."
 211     (n 1 (+ n 2))
 212     ;; KLUDGE: Most implementations don't actually support lists with bignum
 213     ;; elements -- and this is WAY faster on most implementations then declaring
 214     ;; N to be an UNSIGNED-BYTE.
 215     (fixnum n)
 216     (1- n)
 217     n)
 218
 219   (def lastcar (list)
 220       "Returns the last element of LIST. Signals a type-error if LIST is not a
 221 proper list."
 222     nil
 223     nil
 224     (cadr last)
 225     (car fast))
 226
 227   (def (setf lastcar) (object list)
 228       "Sets the last element of LIST. Signals a type-error if LIST is not a proper
 229 list."
 230     nil
 231     nil
 232     (setf (cadr last) object)
 233     (setf (car fast) object)))
 234
 235 (defun make-circular-list (length &key initial-element)
 236   "Creates a circular list of LENGTH with the given INITIAL-ELEMENT."
 237   (let ((cycle (make-list length :initial-element initial-element)))
 238     (nconc cycle cycle)))
 239
 240 (deftype circular-list ()
 241   "Type designator for circular lists. Implemented as a SATISFIES type, so not
 242 recommended for performance intensive use. Main usefullness as the
 243 expected-type designator of a TYPE-ERROR."
 244   `(satisfies circular-list-p))
 245
 246 (defun ensure-car (thing)
 247   "If THING is a CONS, its CAR is returned. Otherwise THING is returned."
 248   (if (consp thing)
 249       (car thing)
 250       thing))
 251
 252 (defun ensure-cons (cons)
 253   "If CONS is a cons, it is returned. Otherwise returns a fresh cons with CONS
 254   in the car, and NIL in the cdr."
 255   (if (consp cons)
 256       cons
 257       (cons cons nil)))
 258
 259 (defun ensure-list (list)
 260   "If LIST is a list, it is returned. Otherwise returns the list designated by LIST."
 261   (if (listp list)
 262       list
 263       (list list)))
 264
 265 (defun remove-from-plist (plist &rest keys)
 266   "Returns a propery-list with same keys and values as PLIST, except that keys
 267 in the list designated by KEYS and values corresponding to them are removed.
 268 The returned property-list may share structure with the PLIST, but PLIST is
 269 not destructively modified. Keys are compared using EQ."
 270   (declare (optimize (speed 3)))
 271   ;; FIXME: possible optimization: (remove-from-plist '(:x 0 :a 1 :b 2) :a)
 272   ;; could return the tail without consing up a new list.
 273   (loop for (key . rest) on plist by #'cddr
 274         do (assert rest () "Expected a proper plist, got ~S" plist)
 275         unless (member key keys :test #'eq)
 276         collect key and collect (first rest)))
 277
 278 (defun delete-from-plist (plist &rest keys)
 279   "Just like REMOVE-FROM-PLIST, but this version may destructively modify the
 280 provided plist."
 281   (declare (optimize speed))
 282   (loop with head = plist
 283         with tail = nil   ; a nil tail means an empty result so far
 284         for (key . rest) on plist by #'cddr
 285         do (assert rest () "Expected a proper plist, got ~S" plist)
 286            (if (member key keys :test #'eq)
 287                ;; skip over this pair
 288                (let ((next (cdr rest)))
 289                  (if tail
 290                      (setf (cdr tail) next)
 291                      (setf head next)))
 292                ;; keep this pair
 293                (setf tail rest))
 294         finally (return head)))
 295
 296 (define-modify-macro remove-from-plistf (&rest keys) remove-from-plist
 297                      "Modify macro for REMOVE-FROM-PLIST.")
 298 (define-modify-macro delete-from-plistf (&rest keys) delete-from-plist
 299                      "Modify macro for DELETE-FROM-PLIST.")
 300
 301 (declaim (inline sans))
 302 (defun sans (plist &rest keys)
 303   "Alias of REMOVE-FROM-PLIST for backward compatibility."
 304   (apply #'remove-from-plist plist keys))
 305
 306 (defun mappend (function &rest lists)
 307   "Applies FUNCTION to respective element(s) of each LIST, appending all the
 308 all the result list to a single list. FUNCTION must return a list."
 309   (loop for results in (apply #'mapcar function lists)
 310         append results))
 311
 312 (defun setp (object &key (test #'eql) (key #'identity))
 313   "Returns true if OBJECT is a list that denotes a set, NIL otherwise. A list
 314 denotes a set if each element of the list is unique under KEY and TEST."
 315   (and (listp object)
 316        (let (seen)
 317          (dolist (elt object t)
 318            (let ((key (funcall key elt)))
 319              (if (member key seen :test test)
 320                  (return nil)
 321                  (push key seen)))))))
 322
 323 (defun set-equal (list1 list2 &key (test #'eql) (key nil keyp))
 324   "Returns true if every element of LIST1 matches some element of LIST2 and
 325 every element of LIST2 matches some element of LIST1. Otherwise returns false."
 326   (let ((keylist1 (if keyp (mapcar key list1) list1))
 327         (keylist2 (if keyp (mapcar key list2) list2)))
 328     (and (dolist (elt keylist1 t)
 329            (or (member elt keylist2 :test test)
 330                (return nil)))
 331          (dolist (elt keylist2 t)
 332            (or (member elt keylist1 :test test)
 333                (return nil))))))
 334
 335 (defun map-product (function list &rest more-lists)
 336   "Returns a list containing the results of calling FUNCTION with one argument
 337 from LIST, and one from each of MORE-LISTS for each combination of arguments.
 338 In other words, returns the product of LIST and MORE-LISTS using FUNCTION.
 339
 340 Example:
 341
 342  (map-product 'list '(1 2) '(3 4) '(5 6))
 343   => ((1 3 5) (1 3 6) (1 4 5) (1 4 6)
 344       (2 3 5) (2 3 6) (2 4 5) (2 4 6))
 345 "
 346   (labels ((%map-product (f lists)
 347              (let ((more (cdr lists))
 348                    (one (car lists)))
 349                (if (not more)
 350                    (mapcar f one)
 351                    (mappend (lambda (x)
 352                               (%map-product (curry f x) more))
 353                             one)))))
 354     (%map-product (ensure-function function) (cons list more-lists))))
 355
 356 (defun flatten (tree)
 357   "Traverses the tree in order, collecting non-null leaves into a list."
 358   (let (list)
 359     (labels ((traverse (subtree)
 360                (when subtree
 361                  (if (consp subtree)
 362                      (progn
 363                        (traverse (car subtree))
 364                        (traverse (cdr subtree)))
 365                      (push subtree list)))))
 366       (traverse tree))
 367     (nreverse list)))