-void error (string s, string location = ""); // Fatal error, exits lilypond!
-void programming_error (string s, string location = "");
-void non_fatal_error (string, string location = "");
-void warning (string s, string location = "");
-void basic_progress (string s, string location = "");
+void error (string s, const string &location = ""); // Fatal error, exits lilypond!
+void programming_error (const string &s, const string &location = "");
+void non_fatal_error (const string&, const string &location = "");
+void warning (const string &s, const string &location = "");
+void basic_progress (const string &s, const string &location = "");