c++: make operator() an alias to the parse function

* data/glr.cc, data/lalr1.cc (operator()): New.
* doc/bison.texi: Update.

NEWS

@@ -14,6 +14,8 @@ GNU Bison NEWS
 
   Variant-based symbols in C++ should use emplace() rather than build().
 
+  In C++ parsers, parser::operator() is now a synonym for the parser::parse.
+
 * Noteworthy changes in release 3.1.91 (2018-10-18) [beta]
 
 ** Bug fixes

data/glr.cc

@@ -166,6 +166,12 @@ m4_pushdef([b4_parse_param], m4_defn([b4_parse_param_orig]))dnl
   {
   }
 
+  int
+  ]b4_parser_class_name[::operator() ()
+  {
+    return parse ();
+  }
+
   int
   ]b4_parser_class_name[::parse ()
   {
@@ -267,6 +273,10 @@ b4_percent_code_get([[requires]])[
     ]b4_parser_class_name[ (]b4_parse_param_decl[);
     virtual ~]b4_parser_class_name[ ();
 
+    /// Parse.  An alias for parse ().
+    /// \returns  0 iff parsing succeeded.
+    int operator() ();
+
     /// Parse.
     /// \returns  0 iff parsing succeeded.
     virtual int parse ();

data/lalr1.cc

@@ -190,6 +190,10 @@ m4_define([b4_shared_declarations],
     ]b4_parser_class_name[ (]b4_parse_param_decl[);
     virtual ~]b4_parser_class_name[ ();
 
+    /// Parse.  An alias for parse ().
+    /// \returns  0 iff parsing succeeded.
+    int operator() ();
+
     /// Parse.
     /// \returns  0 iff parsing succeeded.
     virtual int parse ();
@@ -743,6 +747,12 @@ m4_if(b4_prefix, [yy], [],
     return yyvalue == yytable_ninf_;
   }
 
+  int
+  ]b4_parser_class_name[::operator() ()
+  {
+    return parse ();
+  }
+
   int
   ]b4_parser_class_name[::parse ()
   {

doc/bison.texi

@@ -10714,8 +10714,10 @@ Build a new parser object.  There are no arguments, unless
 Instantiate a syntax-error exception.
 @end deftypeop
 
-@deftypemethod {parser} {int} parse ()
-Run the syntactic analysis, and return 0 on success, 1 otherwise.
+@deftypemethod {parser} {int} operator() ()
+@deftypemethodx {parser} {int} parse ()
+Run the syntactic analysis, and return 0 on success, 1 otherwise.  Both
+routines are equivalent, @code{operator()} being more C++ish.
 
 @cindex exceptions
 The whole function is wrapped in a @code{try}/@code{catch} block, so that