+(defmacro define-variadic-op (operator initial-value)
+ (let ((init-sym (gensym))
+ (dolist-sym (gensym)))
+ `(defun ,operator (&rest args)
+ (let ((,init-sym ,initial-value))
+ (dolist (,dolist-sym args)
+ (setq ,init-sym (,operator ,init-sym ,dolist-sym)))
+ ,init-sym))))
+
+(define-variadic-op + 0)
+(define-variadic-op * 1)
+
+;; - and / work differently from the above macro.
+;; If only one arg is given, it negates it or takes its reciprocal.
+;; Otherwise all the other args are subtracted from or divided by it.
+;; TODO: Use MACROLET when it exists
+(defmacro define-sub-or-div (operator unary-form)
+ `(defun ,operator (x &rest args)
+ (cond
+ ((null args) ,unary-form)
+ (t (dolist (y args)
+ (setq x (,operator x y)))
+ x))))
+
+(define-sub-or-div - (- x))
+(define-sub-or-div / (/ 1 x))
+
+(defun 1+ (x) (+ x 1))
+(defun 1- (x) (- x 1))
+
+(defun truncate (x &optional (y 1))
+ (floor (/ x y)))
+
+(defun integerp (x)
+ (and (numberp x) (= (floor x) x)))
+
+(defun floatp (x)
+ (and (numberp x) (not (integerp x))))
+
+(defun minusp (x) (< x 0))
+(defun zerop (x) (= x 0))
+(defun plusp (x) (< 0 x))
+
+;; TODO: Use MACROLET when it exists