CS 541 Lecture -*- Outline -*-

* Non-local exits
	use the power of continuations to design control-flow constructs

**	call-with-current-continuation
		Value = ... + Expcont

		valE[[(call/cc E1)]]
		= \u\k . valE[[E1]]u
				(\e1 . cases e1 of 
					isProcedure(p) -> (p inExpCont(k) k)
							else error-cont
					end)
		valE[[(call E1 E2)]]
		= \u\k . valE[[E1]]u
				(\e1. cases e1 of
					   isProcedure(p) -> ...
					[] isExpcont(k2) -> valE[[E2]]u
						(\e2. (k2 e2))
					[] err-cont
					end)

**	block and exit constructs (see control handout, second part)
		(block I) declares an exit point

**	goto (Schmidt 9.5)
***		keep command continuations for labels in environment.
			valC[[goto I]] = \u\k.(lookup u [[I]])
***		mutual recursion resolved by fixpoint to construct environment