make Lexer interface a bit more friendly

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@24108 a592a061-630c-0410-9148-cb99ea01b6c8

src/Lexer.cpp

@@ -102,6 +102,8 @@ public:
 	string pushTok;
 	///
 	char commentChar;
+	/// used for error messages
+	string context;
 private:
 	/// non-copyable
 	Pimpl(Pimpl const &);
@@ -878,7 +880,7 @@ Lexer & Lexer::operator>>(bool & s)
 
 // quotes a string, e.g. for use in preferences files or as an argument
 // of the "log" dialog
-string const Lexer::quoteString(string const & arg)
+string Lexer::quoteString(string const & arg)
 {
 	string res;
 	res += '"';
@@ -888,4 +890,22 @@ string const Lexer::quoteString(string const & arg)
 }
 
 
+Lexer & Lexer::operator>>(char const * required)
+{
+	string token;
+	*this >> token;
+	if (token != required) {
+		LYXERR0("Missing '" << required << "'-tag in " << pimpl_->context);
+		pushToken(token);
+	}
+	return *this;
+}
+
+
+void Lexer::setContext(std::string const & str)
+{
+	pimpl_->context = str;
+}
+
+
 } // namespace lyx

src/Lexer.h

@@ -167,6 +167,8 @@ public:
 
 	/// Prints the current token table on the supplied ostream.
 	void printTable(std::ostream &);
+	/// Used to dispaly context information in case of errors.
+	void setContext(std::string const & functionName);
 
 	/// extract string
 	Lexer & operator>>(std::string &);
@@ -181,9 +183,12 @@ public:
 	/// extract bool
 	Lexer & operator>>(bool &);
 
+	/// read and check a required token
+	Lexer & operator>>(char const * required);
+
 	/// Quotes a string so that reading it again with Lexer::next(true)
 	/// gets the original string
-	static std::string const quoteString(std::string const &);
+	static std::string quoteString(std::string const &);
 
 private:
 	/// noncopyable
@@ -206,6 +211,16 @@ private:
 };
 
 
+/// extract something constructable from a string, i.e. a LaTeX length
+template <class T>
+Lexer & operator>>(Lexer & lex, T & t)
+{
+	if (lex.next())
+		t = T(lex.getString());
+	return lex;
+}
+
+
 /** Use to enable multiple exit points.
     This is needed to ensure that the pop is done upon exit from methods
     with more than one exit point or that can return as a response to