line(l)
{ }
+data_error::data_error(const string &s, unsigned l, const data_error &e):
+ runtime_error(format("%s\n%s", e.what(), make_what(s, l, "Referenced here"))),
+ source(s),
+ line(l)
+{ }
+
string data_error::make_what(const string &s, unsigned l, const string &w)
{
if(l)