ehaliewicz

(defmacro -> (init &rest funcs)
  (cond
    ((null funcs) `,init)
    ((eql 'if (car funcs))
     (let* ((gensym (gensym)))
       `(-> (let ((,gensym ,init))
              (if ,gensym (-> ,gensym ,(cadr funcs))
                  (-> ,gensym ,(caddr funcs)))
                 ,@(cdddr funcs)))))
    ((and (consp (car funcs)) (not (eql 'lambda (caar funcs))))

ehaliewicz

(defmacro flip-flop (left right)
  "Evaluates to false until the left test is satisfied.  Then evaluates to true until the right test is satisfied, etc."

  ;; create a collision-safe name for our state variable
  (let ((state-var (gensym)))
    
    ;; create a toplevel variable to keep state of flip-flop
    `(progn 
       (defvar ,state-var nil))

ehaliewicz

;; A couple of silly macros for a language that has defmacro but no tail-recursion

;; the mutual recursion macro is even worse, because you can only really 'call' one of the functions

(defmacro recur (arg-pairs &body body)
  (let ((arg-names (mapcar #'car arg-pairs))  ;; extract loop variable names
        (arg-vals (mapcar #'cadr arg-pairs))) ;; extract start values

    ;; block to return from
    `(block nil