In this talk, I will illustrate these ideas with examples drawn from two parts of the C-- language infrastructure: exception dispatch and procedure calls.  I will focus on the mechanisms that make it possible for you to choose the semantics and cost model you want.  For exceptions, these mechanisms are drawn from both compile-time and run-time interfaces, and together they enable you to duplicate all the established techniques for implementing exceptions.  For procedure calls, the mechanisms are quite different; rather than provide low-level mechanisms that combine to form different kinds of procedure calls, I have found it necessary to extend the compile-time interface to enable direct control of the semantics and cost of procedure calls.  If time permits, I will also explain why our model of procedures is broken and how it must be fixed if it is to support such abstractions as stacklets or first-class continuations.