macro.lisp

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

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

(defmacro random-choice (&rest exprs)
  `(case (random ,(length exprs))
     ,@(let ((key -1))
            (mapcar #'(lambda (expr)
                        `(,(incf key) ,expr))
                    exprs))))

(defmacro avg (&rest args)
  `(/ (+ ,@args) ,(length args)))

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

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