;; Programming Languages, Homework 5 #lang racket (provide (all-defined-out)) ;; so we can put tests in a second file ;; definition of structures for MUPL programs - Do NOT change (struct var (string) #:transparent) ;; a variable, e.g., (var "foo") (struct int (num) #:transparent) ;; a constant number, e.g., (int 17) (struct add (e1 e2) #:transparent) ;; add two expressions (struct ifgreater (e1 e2 e3 e4) #:transparent) ;; if e1 > e2 then e3 else e4 (struct fun (nameopt formal body) #:transparent) ;; a recursive(?) 1-argument function (struct call (funexp actual) #:transparent) ;; function call (struct mlet (var e body) #:transparent) ;; a local binding (let var = e in body) (struct apair (e1 e2) #:transparent) ;; make a new pair (struct fst (e) #:transparent) ;; get first part of a pair (struct snd (e) #:transparent) ;; get second part of a pair (struct aunit () #:transparent) ;; unit value -- good for ending a list (struct isaunit (e) #:transparent) ;; evaluate to 1 if e is unit else 0 ;; a closure is not in "source" programs; it is what functions evaluate to (struct closure (env fun) #:transparent) ;; Problem 1 ;; CHANGE (put your solutions here) ;; Problem 2 ;; lookup a variable in an environment ;; Do NOT change this function (define (envlookup env str) (cond [(null? env) (error "unbound variable during evaluation" str)] [(equal? (car (car env)) str) (cdr (car env))] [#t (envlookup (cdr env) str)])) ;; Do NOT change the two cases given to you. ;; DO add more cases for other kinds of MUPL expressions. ;; We will test eval-under-env by calling it directly even though ;; "in real life" it would be a helper function of eval-exp. (define (eval-under-env e env) (cond [(var? e) (envlookup env (var-string e))] [(add? e) (let ([v1 (eval-under-env (add-e1 e) env)] [v2 (eval-under-env (add-e2 e) env)]) (if (and (int? v1) (int? v2)) (int (+ (int-num v1) (int-num v2))) (error "MUPL addition applied to non-number")))] ;; CHANGE add more cases here [#t (error "bad MUPL expression")])) ;; Do NOT change (define (eval-exp e) (eval-under-env e null)) ;; Problem 3 (define (ifaunit e1 e2 e3) "CHANGE") (define (mlet* lstlst e2) "CHANGE") (define (ifeq e1 e2 e3 e4) "CHANGE") ;; Problem 4 (define mupl-map "CHANGE") (define mupl-mapAddN (mlet "map" mupl-map "CHANGE (notice map is now in MUPL scope)")) ;; Challenge Problem (struct fun-challenge (nameopt formal body freevars) #:transparent) ;; a recursive(?) 1-argument function ;; We will test this function directly, so it must do ;; as described in the assignment (define (compute-free-vars e) "CHANGE") ;; Do NOT share code with eval-under-env because that will make grading ;; more difficult, so copy most of your interpreter here and make minor changes (define (eval-under-env-c e env) "CHANGE") ;; Do NOT change this (define (eval-exp-c e) (eval-under-env-c (compute-free-vars e) null))