src/utils.lisp @ 50ab2f9c5b2f

(in-package #:sand.utils)

;;;; Miscellaneous
(defmacro zap% (place function &rest arguments &environment env)
  "Update `place` by applying `function` to its current value and `arguments`.

  `arguments` should contain the symbol `%`, which is treated as a placeholder
  where the current value of the place will be substituted into the function
  call.

  For example:

  (zap% foo #'- % 10) => (setf foo (- foo 10)
  (zap% foo #'- 10 %) => (setf foo (- 10 foo)

  "
  ;; original idea/name from http://malisper.me/2015/09/29/zap/
  (assert (find '% arguments) ()
    "Placeholder % not included in zap macro form.")
  (multiple-value-bind (temps exprs stores store-expr access-expr)
      (get-setf-expansion place env)
    `(let* (,@(mapcar #'list temps exprs)
            (,(car stores)
             (funcall ,function
                      ,@(substitute access-expr '% arguments))))
      ,store-expr)))

(defmacro recursively (bindings &body body)
  "Execute body recursively, like Clojure's `loop`/`recur`.

  `bindings` should contain a list of symbols and (optional) default values.

  In `body`, `recur` will be bound to the function for recurring.

  Example:

      (defun length (some-list)
        (recursively ((list some-list) (n 0))
          (if (null list)
            n
            (recur (cdr list) (1+ n)))))

  "
  (flet ((extract-var (binding)
           (if (atom binding) binding (first binding)))
         (extract-val (binding)
           (if (atom binding) nil (second binding))))
    `(labels ((recur ,(mapcar #'extract-var bindings)
                ,@body))
      (recur ,@(mapcar #'extract-val bindings)))))

(defmacro dis (arglist &body body)
  "Disassemble the code generated for a `lambda*` with `arglist` and `body`.

  It will also spew compiler notes so you can see why the garbage box isn't
  doing what you think it should be doing.

  "
  `(->> '(lambda* ,arglist
          (declare (optimize speed))
          ,@body)
    macroexpand-1
    (compile nil)
    disassemble))


;;;; Sets
;;; Janky implementation of basic sets.
(defclass hash-set ()
  ((data :initarg :data)))


(defun make-set (&key (test #'eql) (initial-data nil))
  (let ((set (make-instance 'hash-set
                            :data (make-hash-table :test test))))
    (mapcar (curry #'set-add set) initial-data)
    set))


(defun set-contains-p (set value)
  (nth-value 1 (gethash value (slot-value set 'data))))

(defun set-empty-p (set)
  (zerop (hash-table-count (slot-value set 'data))))

(defun set-add (set value)
  (setf (gethash value (slot-value set 'data)) t)
  value)

(defun set-add-all (set seq)
  (map nil (curry #'set-add set) seq))

(defun set-remove (set value)
  (remhash value (slot-value set 'data))
  value)

(defun set-remove-all (set seq)
  (map nil (curry #'set-remove set) seq))

(defun set-clear (set)
  (clrhash (slot-value set 'data))
  set)

(defun set-random (set)
  (if (set-empty-p set)
    (values nil nil)
    (loop :with data = (slot-value set 'data)
          :with target = (random (hash-table-count data))
          :for i :from 0
          :for k :being :the :hash-keys :of data
          :when (= i target)
          :do (return (values k t)))))

(defun set-pop (set)
  (multiple-value-bind (val found) (set-random set)
    (if found
      (progn
        (set-remove set val)
        (values val t))
      (values nil nil))))


(defmethod print-object ((set hash-set) stream)
  (print-unreadable-object (set stream :type t)
    (format stream "~{~S~^ ~}"
            (hash-keys (slot-value set 'data)))))


;;;; Iterate
(defmacro-clause (AVERAGING expr &optional INTO var)
  (with-gensyms (count)
    (let ((average (or var (gensym "average"))))
      `(progn
        (for ,average
             :first ,expr
             ;; continuously recompute the running average instead of keeping
             ;; a running total to avoid bignums when possible
             :then (/ (+ (* ,average ,count)
                         ,expr)
                      (1+ ,count)))
        (for ,count :from 1)
        ,(when (null var)
           ;; todo handle this better
           `(finally (return ,average)))))))

(defmacro-clause (TIMING time-type &optional SINCE-START-INTO var PER-ITERATION-INTO per)
  (let ((timing-function (ecase time-type
                           ((real-time) #'get-internal-real-time)
                           ((run-time) #'get-internal-run-time)))
        (since (or var (gensym))))
    (with-gensyms (start-time current-time previous-time)
      `(progn
        (with ,start-time = (funcall ,timing-function))
        (for ,current-time = (funcall ,timing-function))
        (for ,previous-time :previous ,current-time :initially ,start-time)
        (for ,since = (- ,current-time ,start-time))
        ,(when per
           `(for ,per = (- ,current-time ,previous-time)))
        ,(when (and (null var) (null per))
           `(finally (return ,since)))))))


;;;; Queues
;;; From PAIP (thanks, Norvig).

(deftype queue () '(cons list list))

(declaim (inline queue-contents make-queue
                 enqueue dequeue
                 queue-empty-p queue-append))


(defun* queue-contents ((q queue))
  (:returns list)
  (cdr q))

(defun* make-queue ()
  (:returns queue)
  (let ((q (cons nil nil)))
    (setf (car q) q)))

(defun* enqueue ((item t) (q queue))
  (:returns queue)
  (setf (car q)
        (setf (rest (car q))
              (cons item nil)))
  q)

(defun* dequeue ((q queue))
  (:returns t)
  (prog1
      (pop (cdr q))
    (if (null (cdr q))
      (setf (car q) q))))

(defun* queue-empty-p ((q queue))
  (:returns boolean)
  (null (queue-contents q)))

(defun* queue-append ((q queue) (l list))
  (:returns queue)
  (when l
    (setf (car q)
          (last (setf (rest (car q))
                      l))))
  q)