Added [has_default_reduction] to the incremental API.

CHANGES

+2015/09/29:
+Added [has_default_reduction] to the incremental API.
+
 2015/09/25:
 Modified the meaning of --canonical to allow default reductions to take
 place. There implies no loss of precision in terms of lookahead sets,

doc/main.tex

@@ -2145,6 +2145,18 @@ current lookahead token. It is legal to invoke this function only after at
 least one token has been offered to the parser via \verb+offer+. In other
 words, it is illegal to invoke it in an initial state.
 
+%% val has_default_reduction
+
+\begin{verbatim}
+  val has_default_reduction: env -> bool
+\end{verbatim}
+
+The function \verb+has_default_reduction+
+tells whether the parser is about to perform a default reduction.
+In particular, when applied to an environment \verb+env+ taken from a result of
+the form \verb+AboutToReduce (env, prod)+, it tells whether the reduction
+that is about to take place is a default reduction.
+
 % ------------------------------------------------------------------------------
 
 \subsection{Inspection API}

src/IncrementalEngine.ml

@@ -100,6 +100,13 @@ module type INCREMENTAL_ENGINE = sig
 
   val positions: env -> Lexing.position * Lexing.position
 
+  (* This tells whether the parser is about to perform a default reduction.
+     In particular, when applied to an environment taken from a result of
+     the form [AboutToReduce (env, prod)], this tells whether the reduction
+     that is about to take place is a default reduction. *)
+
+  val has_default_reduction: env -> bool
+
 end
 
 (* This signature is a fragment of the inspection API that is made available

src/engine.ml

@@ -577,5 +577,19 @@ module Make (T : TABLE) = struct
     assert (startp != dummy_pos && endp != dummy_pos);
     startp, endp
 
+  (* --------------------------------------------------------------------------- *)
+
+  (* Access to information about default reductions. *)
+
+  (* We can make this a function of states, or a function of environments. For
+     now, the latter appears simpler. *)
+
+  let has_default_reduction env : bool =
+    T.default_reduction
+      env.current
+      (fun _env _prod -> true)
+      (fun _env -> false)
+      env
+
 end