Design of CMU Common Lisp.pdf - Common Lisp.net

variables.
Environment analysis emits cleanup code for local exits and markers for non-local exits.
A non-local exit is a control transfer from one environment to another. In a non-local exit, we must close
over the continuation that we transfer to so that the exiting function can find its way back. We indicate the need
to close a continuation by placing the continuation structure in the closure and also pushing it on a list in the
environment structure for the target of the exit. [### To be safe, we would treat the continuation as a set closure
variable so that we could invalidate it when we leave the dynamic extent of the exit point. Transferring control
to a meaningless stack pointer would be apt to cause horrible death.]
Each local control transfer may require dynamic state such as special bindings to be undone. We represent
cleanup actions by funny function calls in a new block linked in as an implicit MV-PROG1.
34