[camlp4] Add an example about the "debug" syntax extension.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@8611 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

1 files changed, 37 insertions, 0 deletions

diff --git a/camlp4/examples/debug_extension.ml b/camlp4/examples/debug_extension.ml
new file mode 100644
index 000000000..21696e4a9
--- /dev/null
+++ b/camlp4/examples/debug_extension.ml
@@ -0,0 +1,37 @@
+(*
+ * No debugging code at all:
+ *   $ camlp4o -parser Camlp4DebugParser debug_extension.ml
+ *   true
+ * Debugging code for lexing:
+ *   $ STATIC_CAMLP4_DEBUG='lexing' camlp4o -parser Camlp4DebugParser debug_extension.ml
+ *  let () =
+ *    if Camlp4.Debug.mode "lexing"
+ *    then Debug.printf "lexing" "TOKEN: Int %d" (2 * 21)
+ *    else ()
+ *  in true
+ *
+ * Debugging code for lexing and parsing:
+ *   $ STATIC_CAMLP4_DEBUG='lexing:parsing' camlp4o -parser Camlp4DebugParser debug_extension.ml
+ *   let () =
+ *     if Camlp4.Debug.mode "lexing"
+ *     then Debug.printf "lexing" "TOKEN: Int %d" (2 * 21)
+ *     else () in
+ *   let () =
+ *     if Camlp4.Debug.mode "parsing"
+ *     then Debug.printf "parsing" "RULE: ..."
+ *     else ()
+ *   in true
+ *
+ * Debugging code for any section:
+ *  $ STATIC_CAMLP4_DEBUG='*' camlp4o -parser Camlp4DebugParser debug_extension.ml
+ *  ... same output as above ...
+ *
+ * When you program is compiled you can use the CAMLP4_DEBUG variable to
+ * activate some debugging sections.
+ *
+ * CAMLP4_DEBUG_FILE manage where messages goes (default is stderr).
+ *)
+
+camlp4_debug lexing  "TOKEN: Int %d" (2 * 21) in
+camlp4_debug parsing "RULE: ..." in
+true