You do not need to handin this tutorial to the handin server (it is just for practice) There are no submission tests (or marks for this tutorial). There will be a solution posted, but I suggesting trying the exercises before looking at the solution.

There is skeleton file

Free variables

Complete the function free-vars below that finds all free variables in a given Exp expression. Note that environments here are sets of bound identifiers implemented with hash tables.

(test (free-vars (numE 3) empty-env) empty-env)
(test (free-vars (plusE (varE 'x) (numE 3)) empty-env)
      (extend 'x empty-env))
(test (free-vars (plusE (varE 'x) (numE 3))
                 (extend 'x empty-env)) empty-env)
(test (free-vars (let1E 'x (numE 3) (plusE (varE 'x) (numE 3)))
                 empty-env) empty-env)
(test (free-vars (let1E 'x (numE 3) (plusE (varE 'x) (numE 3)))
                 (extend 'x empty-env)) empty-env)
(test (free-vars (let1E 'x (varE 'y) (plusE (varE 'x) (numE 3)))
                 (extend 'x empty-env)) (extend 'y empty-env))
(test (free-vars (lamE 'x  (plusE (varE 'x) (numE 3)))
                 (extend 'x empty-env)) empty-env)
(test (free-vars (appE (varE 'x) (varE 'x)) empty-env)
      (extend 'x empty-env))

Macros

Add a syntax rule for `nand` (negated and) that supports short circuiting. Note that by definition of short-circuiting, code coverage is impossible for the tests themselves.

(define-syntax nand
  (syntax-rules () [(_ arg ...)  ....]))

(test (nand #f) #t)
(test (nand #t (begin (/ 1 0) #t)) #f)
(test (nand #f #t (eq? (/ 1 0) 0)) #f)