`INIT $RAT-OVERFLOW = CX::Warn` will produce a warning whenever a switch to Num happens.

`INIT $RAT-OVERFLOW = Exception` will throw an exception whenever a switch to Num would happen.

If you want to define your own behaviour, you can. For instance:

class ZeroOrInf { method UPGRADE-RAT(Int $nu, Int $de) { $nu > $de ?? Inf !! 0 } } INIT $*RAT-OVERFLOW = ZeroOrInf

would either convert the value to `Inf`if too large, or to `0` if too small.