#+Title: debug messages
#+Property: session *R*
#+Property: prologue (format "print(\"entering %s\")" (get-current-name))

An elisp block to simplify the =:prologue= definition.
#+begin_src emacs-lisp
  (defun get-current-name ()
    (save-excursion
      (goto-char org-babel-current-src-block-location)
      (while (and (forward-line -1)
                  (looking-at org-babel-multi-line-header-regexp)))
      (when (looking-at org-babel-src-name-w-name-regexp)
        (org-no-properties (match-string 3)))))
#+end_src

Two blocks with simple assignments.

#+name: block-1
#+begin_src R
  x <- 2 + 2
#+end_src

#+name: block-2
#+begin_src R
  y <- x + x
#+end_src

Execute the whole buffer =C-c C-v b= to see the prologue in action.