CS217 Assignment 7, Due Monday, May 15, 2000

1. Starting with continuation-passing interpreter interp4-1cps.scm, implement and test while-do. Study implementations of varassign-exp and begin-exp to get the idea.

   Recall the grammar

   (expression
     ("while" expression "do" expression)
     while-do-exp)
   

   and code

   (while-do-exp (test exp)
     (eval-while-do test exp env))
   

   where

   (define eval-while-do
     (lambda (test exp env)
       (if (true-value? (eval-expression test env))
   	(begin
   	  (eval-expression exp env)
   	  (eval-while-do test exp env))
   	1)))
   

   Or see interp3-7loop.scm.

   This has to be translated to CPS and a while-do-cont continuation has to be constructed.

2. Examine and experiment with Scheme.java, a call-by-value interpreter in Java that parses and evaluates list syntax. Compile with

   javac Scheme.java
   

   and run with

   java Scheme
   

   or

   java Scheme file.scm
   

3. Complete and test definition of If class.
4. Modify

   let index = proc (n, l)
                 letrec loop(l) = if null?(l) then raise sub1(0)
                                  else if equal?(n, car(l)) then 0
                                  else add1((loop cdr(l)))
                 in try (loop l) handle proc (x) x
   in begin
        print((index 1 list(2, 3, 4)));
        print((index 3 list(2, 3, 4)));
        (index 4 list(2, 3, 4))
      end
   

   to add parameters lo and hi to index, so

   (index n lst lo hi) => index of n in lst if n occurs in pos n to m
                          else -1
   

   Have your expression print the results of several calls, which test index in all cases. Use interp4-4exc.scm