src/utils.lisp @ 800b4dcae88c

(in-package #:mazes.utils)

(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 in-context (&body body)
  `(prog1
    (push-matrix)
    (progn ,@body)
    (pop-matrix)))


(defun dividesp (n divisor)
  "Return whether `n` is evenly divisible by `divisor`."
  (zerop (mod n divisor)))