For the above we will be learning a general CPS transformation technique that uses a single continuation with one argument. Each continuation takes as many arguments as are needed for the information that is specific to it. In normal programming there is a single implicit continuation.
Exception handlers are a kind of implicit failure continuation.
In some applications there may be even more than two continuations, implicit or explicit. If more than one continuation is common, as in the lookup example, it is often clearest to use explicit continuation passing. Many procedures need to return multiple values. There are a few ways to do this. Return a data structure containing the values, as above.