instances for bottom?

I was wondering whether the method by which default types are chosen for unresolved overloading could be made available to the programmer. It seems that if we consider the overlapping instances: class x instance Int instance Float instance x x overlaps with Int and Float... I was wondering if it were possible to determine that type inferance had failed... like with: show (read x :: y) Here y (the type of read x) has no type... and does not match _any_ instance apart from 'x'... so would it not be possible to have an instance for "no type"? perhaps: instance _|_ ... Keean.