RosettaCodeData/Task/Factorial/Order/factorial-1.order

#include <order/interpreter.h>

#define ORDER_PP_DEF_8fac                     \
ORDER_PP_FN(8fn(8N,                           \
                8if(8less_eq(8N, 0),          \
                    1,                        \
                    8mul(8N, 8fac(8dec(8N))))))

ORDER_PP(8to_lit(8fac(8)))    // 40320