3.5.12 Dynamic extent and the dynamic environment

For a procedure call, the time between when it is initiated and when it returns is called its dynamic extent. In Scheme, call-with-current-continuation allows reentering a dynamic extent after its procedure call has returned. Thus, the dynamic extent of a call may not be a single, connected time period.

Some operations described in the report acquire information in addition to their explicit arguments from the dynamic environment. For example, call-with-current-continuation accesses an implicit context established by dynamic-wind, and the raise procedure accesses the current exception handler.

The operations that modify the dynamic environment do so dynamically, for the dynamic extent of a call to a procedure like dynamic-wind or with-exception-handler. When such a call returns, the previous dynamic environment is restored. The dynamic environment can be thought of as part of the dynamic extent of a call. Consequently, it is captured by call-with-current-continuation, and restored by invoking the escape procedure it creates.