Nice cleanup of myocamlbuild.ml.

src/myocamlbuild.ml

@@ -27,46 +27,43 @@ let fancy () : bool =
   mark_tag_used "fancy_parser";
   Tags.mem "fancy_parser" (tags_of_pathname "")
 
-let parser_rule () =
+let compile_messages grammar messages target =
+  rule
+    "compile a custom table of messages"
+    ~prod:target
+    ~deps:[ grammar; messages ]
+    (fun env _ ->
+      Cmd(S[
+        !Options.ocamlyacc; (* menhir *)
+        (* no additional flags; may allow them in the future *)
+        P (env grammar);
+        A "--compile-errors"; P (env messages);
+        Sh ">"; Px (env target);
+      ]))
+
+let parser_configuration () =
+  (* Create [parser.mly] by copying the appropriate source file. *)
   copy_rule "create parser.mly"
     (* source: *)
     (if fancy() then "fancy-parser.mly" else "yacc-parser.mly")
     (* target: *)
     "parser.mly"
-
-let driver_rule () =
+  ;
+  (* Create [Driver.ml] by copying the appropriate source file. *)
   copy_rule "create Driver.ml" 
     (* source: *)
     (if fancy() then "fancyDriver.ml" else "yaccDriver.ml")
     (* target: *)
     "Driver.ml"
-
-(* ---------------------------------------------------------------------------- *)
-
-(* The file [FancyParserMessages.ml] is generated by Menhir based on
-   [fancy-parser.messages], which is maintained by hand. Of course,
-   this is possible only in stage 2 of the bootstrap process, since
-   Menhir is required. *)
-
-let messages_rule () =
-  if Tags.mem "fancy_parser" (tags_of_pathname "") then
-    (* The target. *)
-    let prod = "FancyParserMessages.ml" in
-    (* The two source files. *)
-    let messages = "fancy-parser.messages"
-    and grammar = "parser.mly" in
-    (* The production rule. *)
-    rule
-      "fancy parser messages"
-      ~prod:prod
-      ~deps:[ messages; grammar ]
-      (fun env _ ->
-        Cmd(S[
-          !Options.ocamlyacc; (* menhir *)
-          P (env grammar);
-          A "--compile-errors"; P (env messages);
-          Sh ">"; Px (env prod);
-        ]))
+  ;
+  (* In the fancy case, use Menhir to generate [FancyParserMessages.ml] based
+     on [fancy-parser.messages], which is maintained by hand. *)
+  if fancy() then
+    compile_messages
+      (* sources: *)
+      "parser.mly" "fancy-parser.messages"
+      (* target: *)
+      "FancyParserMessages.ml"
 
 (* ---------------------------------------------------------------------------- *)
 
@@ -75,9 +72,7 @@ let messages_rule () =
 let () =
   dispatch (function After_rules ->
     (* Add our rules after the standard ones. *)
-    parser_rule();
-    driver_rule();
-    messages_rule();
+    parser_configuration();
     flags();
   | _ -> ()
   )