Ulex 0.7 (required by PXP) needs the following patch to build on ocaml 
3.09.0.

Alex

diff -Naur ulex-0.7/mk_pa_ulex.ml ulex-0.7-deit/mk_pa_ulex.ml
--- ulex-0.7/mk_pa_ulex.ml      2005-05-24 17:16:51.000000000 +0200
+++ ulex-0.7-deit/mk_pa_ulex.ml 2005-10-28 10:07:48.000000000 +0200
@@ -1,5 +1,5 @@
  let s = float_of_string (String.sub (Sys.ocaml_version) 0 4) in
-if (s <= 3.09) then (
+if (s < 3.09) then (
    print_endline "Old camlp4 (loc)";
    Sys.command "sed s/_loc/loc/ < pa_ulex.ml.src > pa_ulex.ml"
  )