| Library | File | Standard Definitions |
| typedef unsigned char | xbool; |
| # define xtrue | ((xbool) 0x01) |
| # define xfalse | ((xbool) 0x00) |
| # define xboolnil | ((xbool) 0x80) |
| Boolean type. | |
| typedef int | xint; |
| # define xintnil | ((xint) 0x80000000) |
| Integer type. | |
| typedef double | xreal; |
| # define xrealnil | ((xreal) 1E126) |
| Real number type. | |
| # define optional | |
| Indicates that value can be nil | |