I've tweaked  the GNU id-utils to also support SML and lisp.
(Should work equally well for Ocaml, I think.  Let me know if not.)

The source tarball (and a Debian binary .deb) are up at:
  http://muq.org/~cynbe/ml/smlnj-hacking-idutils.html

Synopsis for anyone unfamiliar with the id-utils:

    A keystroke or two in emacs or vi gives lightning-fast access to all
    occurrences of a given identifier in the codebase.  Great for looking
    up definitions, checking all uses after a redefinition, finding a
    typical invocation, and so forth.  Valuable for reading any codebase
    over ten kilolines, and indispensable for multi-megaline codebases
    (where etags simply halts and catches fire).

    I'm a frank addict.

 --Cynbe