thread/postfix macro

(defmacro -> (init &rest funcs)
  (cond
    ((null funcs) `,init)
    ((consp (car funcs))
     (let* ((gensym (gensym))
            (func (recursive-replace '_ `,gensym (car funcs))))
       `(let ((,gensym ,init)) (-> ,func ,@(cdr funcs)))))
     (t `(-> (,(car funcs) ,init) ,@(cdr funcs)))))

(defun recursive-replace (item replace form)
  (loop for form in form collect
       (if (consp form)
           (recursive-replace item replace form)
           (if (eql form item)
               replace
               form))))


(labels ((square (x) (* x x)))
   (-> 2 square sqrt))

-> 2.0

(-> 2 (* _ _) (sqrt _))

-> 2.0

;; signum returns the sign of the given number
(-> -3 signum plusp (if _ (print "true")
                          (print "false")))

-> false

(-> 3 signum plusp (if _ (print "true")
                         (print "false")))

-> true