Program 1

Recall the definition of the AExp datatype from class. Consider adding the let construct to this language and creating the new datatype, ALetExp. A let form looks like (let (var val) body) where var is a variable and val and body are expressions (ALetExp's). An sample expression is (let (x (1 + 2)) (x * x)) Note that you are only asked to write a parser, not an interpreter. Turn in all the code needed to parse this extended language. Your parser is due by 11am on 2000-09-11. Email the code to the TA before, and submit it in print at, the start of class. You may have to make some assumptions about the syntax of programs; document them! Challenge: Try to formulate a reduction rule for let. A reduction rule specifies how computations are converted into values. For example, the reduction rule for + says to reduce the two sub-expressions to numeric values, then perform Scheme addition on the resulting numbers. Try to formulate one for let. Be concise, but also be correct! (Warning: If you haven't done this before: it's trickier than you think.)