org-macros in header arguments of org-babel?

Question

Is there a way to specify org-macros that can be used in header arguments of org-babel? One application is to specify the figure path. For instance I want to define:

#+macro: folder figures_here

in the preamble, and then later,

#+begin_src R :results graphics :file {{{folder}}}/figure1.svg

and so on. This does not seem to work - is there another way such a macro can be specified, or specifically for designating the output directory there is a better way?

Answer 1

The expansion of org-macros in source block header arguments is not built into org-mode. See that related SO question.

But, you can add it with the following Elisp snippet.

(defun my-org-babel-expand-macros (params)
  "Replace org macros in all header argument values."
  (mapc
   (lambda (par)
     (let ((templates org-macro-templates)
           (val (cdr par)))
       (when (stringp val)
         (setcdr par 
                 (with-temp-buffer
                   (insert val)
                   (org-macro-replace-all templates)
                   (buffer-string))))))
   params))

(advice-add 'org-babel-process-params :filter-return #'my-org-babel-expand-macros)