[BABEL] Tangling to a hierarchy of files?

[Christopher Maier <christopher.maier@gmail.com>]

I've been experimenting with literate programming using Org mode recently and am
really enjoying it.  I am trying to figure out the best way to create a nested
hierarchy of tangled files from a single Org file, and am not sure the best way
to go about it.

I know that, for example, this block, when tangled, will produce a file
"foo.clj" in the same directory as my Org file... so far so good.

#+begin_src clojure :tangle foo.clj
  (ns foo)
  
  (defn my-inc [x]
    (+ x 1))
#+end_src

However, I would like to be able to do something like this:

#+begin_src clojure :tangle src/foo.clj
  (ns foo)
  
  (defn my-inc [x]
    (+ x 1))
#+end_src

(I'm trying to automatically generate a Leiningen project for Clojure, if that
helps any.)

If I tangle an Org file that contains a block like this, and I haven't already
created a "src" directory, then I get an error ("Opening output file: No such
file or directory...").

I could create a shell script block in my file that will create whatever
directory hierarchy I need, but it looks like I'd have to manually execute that
prior to tangling my source code.  I've seen some examples on the mailing list
using Emacs Lisp code blocks to set up a custom org-babel-pre-tangle-hook, but
it still seems that there's a manual execution step required.

Is there a better (maybe already built-in?) way to achieve this?  Ideally, I'd
eventually like to set things up so that I could invoke a single function that
would create the file hierarchy, tangle the files, generate documentation, and
then run tests and other build-related stuff.  Is that possible without leaving
Org?

Thanks in advance for any help.