<>.lisp

(defun print-intermediate (x)
  (format t"I got intermediate val: ~d~%" x)
  nil)
(defun traverse-rec (body fn)
  (if (listp body)
      (or (funcall fn body) (mapcar (lambda (sub) (traverse-rec sub fn)) body)) ;; note: this means fn can't return an explicitly-nil value
      body))
(defmacro prog<> (body)
  (let* ((prog1-sym (gensym "prog1"))
         prog1-target
         (newbody
          (traverse-rec body
                        (lambda (sub)
                          (if (and (= (length sub) 2)
                                   (equal (car sub) '<>))
                              (progn
                               (setf prog1-target (cadr sub))
                               prog1-sym)
                              nil)))))
    `(let ((,prog1-sym ,prog1-target)) (prog1 ,prog1-sym ,newbody))))

(defvar a (prog<> (print-intermediate (<> 1))))
(princ a)

out.txt

I got intermediate val: 1
1