Document [current_state_number].

doc/main.tex

@@ -2548,6 +2548,20 @@ than or equal to the number of elements in the stack, \verb+None+ is returned.
 \verb+get+ is implemented using \verb+pop_many+ and \verb+top+: its time
 complexity is $O(i)$.
 
+%% val current_state_number
+
+\begin{verbatim}
+  val current_state_number: 'a env -> int
+\end{verbatim}
+
+\verb+current_state_number env+ is the integer number of the automaton's
+current state. Although this number might conceivably be obtained via the
+functions~\verb+top+ and \verb+number+, using \verb+current_state_number+ is
+preferable, because this method works even when the automaton's stack is empty
+(in which case the current state is an initial state, and \verb+top+ returns
+\verb+None+). This number can be passed as an argument to a \verb+message+
+function generated by \verb+menhir --compile-errors+.
+
 %% val equal
 
 \begin{verbatim}

src/IncrementalEngine.ml

@@ -282,10 +282,10 @@ module type INCREMENTAL_ENGINE = sig
 
   val get: int -> 'a env -> element option
 
-  (* [current_state_number env] returns (the integer number of) the automaton's
-     current state. This works even if the automaton's stack is empty, in which
-     case the current state is an initial state. This number can be used as an
-     argument to a [message] function that was generated by [menhir
+  (* [current_state_number env] is (the integer number of) the automaton's
+     current state. This works even if the automaton's stack is empty, in
+     which case the current state is an initial state. This number can be
+     passed as an argument to a [message] function generated by [menhir
      --compile-errors]. *)
 
   val current_state_number: 'a env -> int