Modified [EngineTypes] and [Engine] to clarify the role of the flag [log].

src/engine.ml

@@ -275,7 +275,8 @@ module Make (T : TABLE) = struct
   (* Here, the lookahead token CAN be [error]. *)
 
   and initiate env =
-    Log.initiating_error_handling();
+    if log then
+      Log.initiating_error_handling();
     let env = { env with error = true } in
     HandlingError env
 
@@ -304,14 +305,16 @@ module Make (T : TABLE) = struct
 
     (* This state is capable of shifting the [error] token. *)
 
-    Log.handling_error env.current;
+    if log then
+      Log.handling_error env.current;
     shift env please_discard terminal value s'
 
   and error_reduce env prod =
 
     (* This state is capable of performing a reduction on [error]. *)
 
-    Log.handling_error env.current;
+    if log then
+      Log.handling_error env.current;
     reduce env prod
       (* Intentionally calling [reduce] instead of [announce_reduce].
          It does not seem very useful, and it could be confusing, to

src/engineTypes.ml

@@ -228,10 +228,8 @@ module type TABLE = sig
   (* The comments below indicate the conventional messages that correspond
      to these hooks in the code-based back-end; see [CodeBackend]. *)
 
-  (* If the flag [log] is false, then the logging functions are guaranteed
-     to do nothing, so it is not necessary to call them. If [log] is true,
-     the logging functions may or may not have an effect. This flag is
-     logically superfluous, but saves time in the table-based back-end. *)
+  (* If the flag [log] is false, then the logging functions are not called.
+     If it is [true], then they are called. *)
 
   val log : bool