Control provides a framework for creating and manipulating delimited continuations and delimited dynamic variables.
In particular, Control implements the
shift control operator. Given a mark on the stack (placed there by
shift will "cut" the stack from the context sending
#shift down to that mark, and turn that chunk of stack into a function.
The problems in the interaction between dynamic variables and delimited continuations are best described elsewhere. Control's delimited dynamic variables play nicely with control operators.
Smalltalk's resumable exceptions form the basis for the library.