foo.lisp

(require :sb-cltl2)

(defun foo ()
  (print 'hello))

(defun rep (n thunk)
  (loop :repeat n :do (funcall thunk)))

(define-compiler-macro rep (&whole form n thunk &environment env)
  (if (constantp n env)
    (let ((x (eval (sb-cltl2:macroexpand-all n env))))
      (if (< x 5)
        (let ((thunk% (gensym "thunk")))
          (format t "unrolling loop to become: ")
          (print `(let ((,thunk% ,thunk))
                    ,@(loop :repeat x :collect `(funcall ,thunk%)))))
        form)) ; don't unroll TOO much
    form))

(defun a ()
  (rep 4 #'foo))

(defun b ()
  (rep (+ 1 2) #'foo))

(defun c ()
  (symbol-macrolet ((x '(2)))
    (rep (car x) #'foo)))