CSE526: Principles of Programming Languages
			      Scott Stoller
		    hw7: Iswim-like languages
			version: 11am,17mar2004
			   due: 27apr2004

1. This problem is a variant of [Reynolds, Exercise 13.3].  In summary,
Exercise 13.3 describes reversible references, and asks you to
implement reversible references using the ordinary references defined
in Sections 13.{1,2} as an extension to the syntax and evaluation
semantics in Section 11.2.  You do not need to do this.  Instead, you
should...

Directly extend the syntax and evaluation semantics in Section 11.2 to
include reversible references.  

Notes:

(1) the resulting language should not include ordinary references.

(2) you may change the evaluation semantics in Section 11.2 in any
necessary way, e.g., by changing the definition of state or
configuration.  You are not limited to adding inference rules.


There is no homework problem for chapter 15.  The project will give you
enough experience with typing rules.