configure: Detect camlp4 and bail if not available.

diff --git a/configure.ac b/configure.ac
index 177a166..dddaf3c 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -52,6 +52,12 @@ if test "$OCAMLFIND" = "no"; then
     AC_MSG_ERROR([You must install OCaml findlib (ocamlfind)])
 fi
 
+dnl Check for camlp4.
+AC_PROG_CAMLP4
+if test "$CAMLP4" = "no"; then
+    AC_MSG_ERROR([You must install the OCaml 'camlp4' preprocessor package])
+fi
+
 dnl Check for all OCaml packages.
 AC_CHECK_OCAML_PKG([lablgtk2])
 if test "$OCAML_PKG_lablgtk2" = "no"; then