I was browsing through the math-toolkit and noticed a neat way of type-a-fying mathematical constants. I had been doing something similar but with static constants in a struct which required definitions to be linked into each translation unit. Here's a simplified version: #define DEFINE_MATH_CONSTANT(name, x, exp)\ template <class T> inline T name() { static const T result = ::boost::lexical_cast<T>(STRINGIZE(JOIN(x, JOIN(e, exp)))); return result; } template <> inline float name<float>() { return JOIN(JOIN(x, JOIN(e, exp)), F); } template <> inline double name<double>() { return JOIN(x, JOIN(e, exp)); } template <> inline long double name<long double>() { return JOIN(JOIN(x, JOIN(e, exp)), L); } But then I went to do something like: DEFINE_MATH_CONSTANT(h, 6.62606896, -34) And got: error: pasting "e" and "-" does not give a valid preprocessing token error: exponent has no digits error: invalid suffix "F" on integer constant ... etc. etc. So I modified it to this: #define DEFINE_MATH_CONSTANT(name, x, sign, exp)\ template <class T> inline T name()\ {\ static const T result = ::boost::lexical_cast<T>(STRINGIZE(JOIN(x, JOIN(JOIN(0e, sign), exp))));\ return result;\ }\ template <> inline float name<float>()\ { return JOIN(JOIN(x, JOIN(JOIN(0e, sign), exp)), F); }\ template <> inline double name<double>()\ { return JOIN(x, JOIN(JOIN(0e, sign), exp)); }\ template <> inline long double name<long double>()\ { return JOIN(JOIN(x, JOIN(JOIN(0e, sign), exp)), L); } and now: DEFINE_MATH_CONSTANT(h, 6.62606896, -, 34) works as expected. If its not too complicated, can someone walk through the substitution process that the preprocessor is performing and highlight why pasting 'e' and '-' gives rise to an error where '0e' and '-' does not? I took a brief look at the standard and I'm guiessing it has to do with ## resulting in an invalid preprocessing token (with "e-" being invalid where "0e-" isn't??). The author of math-toolkit might want to implement such a solution as well if negative exponents could potentially be used in defining math constants. Cheers, Chris