>Can ocaml be made to compile files with extensions other than .ml?  I want
to >use both SML and ocaml and have Emacs go into the right mode based on
the file >extension (yes I know I can indicate the proper mode to Emacs by
putting >something in a comment).

Use the -impl option, e.g.,

  ocamlc -c -impl foo.caml

You can use -intf to compile interfaces too, but I bet you will have
problems unless interfaces end with .mli.

--FC