6.001 Final Exam ReviewStudy ResourcesTopicsFall 1998 Exam: True/FalseBox-and-PointersSlide 6Listless FunOrders of GrowthEnvironmental TriviaWrite the Scheme Code to Create the Following Environment DiagramSlide 11OOPsMeandering StreamsFall 1998 Exam: InterleavingsSlide 15foreach special formSlide 17Slide 18Slide 196.001 Final Exam ReviewSpring 2005By Gerald DalleyStudy Resources•Lectures–2005-05-12 lecture had some good summary portions (+ preview of future courses)•Previous exams–Skip any problems with ec-eval or (goto …)•Online tutor•Tutorial problemsTopics•Scheme•Procedures and recursion•Orders of growth•Data abstractions•Higher-order procedures•Program methodology•Symbols and quotation•Abstract data types•Mutation•Environment model•Object-oriented systems•Interpretation / evaluation•Lazy evaluation•Asynchronous computingFall 1998 Exam: True/False•If the Scheme evaluator supports the delay and force special forms, it is possible for the Scheme user to implement cond as a simple procedure without additional extensions to the evaluator.–False: delay requires that the user explicitly mark delayed expressions. The cond “procedure” needs to implicitly delay all of its arguments.•Deadlock can occur between two processes that are running in parallel if a mutual exclusion approach is used (such as the synchronization approach discussed in class) in which both processes try to gain access to a single shared resource.–False: we need two shared resources for deadlock (given the scheme presented in class)Box-and-Pointers(define mob '(1 2 3 4))(set-cdr! (cdddr mob) mob)(define (l x y) (set-car! x y) (set-car! y x))(l mob (cddr mob))(l (cdr mob) (cdddr mob))mobBox-and-Pointers(define mob '(1 2 3 4))(set-cdr! (cdddr mob) mob)(define (l x y) (set-car! x y) (set-car! y x))(l mob (cddr mob))(l (cdr mob) (cdddr mob))mob1324mobListless Fun•What is the final value of z? (define x '(1 2 3))(define y '(4 5 6))(define z (list (list (list x y)) x 7))(set-cdr! (cddr x) (third z))•((((1 2 3 . 7) (4 5 6))) (1 2 3 . 7) 7)Orders of Growth(define (find-e n) (if (= n 0) 1. (+ (/ (fact n)) (find-e (- n 1))))) •Time: Θ(n2) •Space: Θ(n) (define (fast-expt x n) (cond ((= n 0) 1) ((even? n) (fast-expt (* x x) (/ n 2))) (else (* x (fast-expt x (- n 1)))))) •Time: Θ(log n) •Space: Θ(log n)Environmental Trivia•To drop a frame…(let ((…) …) …)(proc …)•To create a double-bubble…(let ((…) …) …) if desugaring(lambda (…) …)(define (foo …) …)•Environments form what type of a graph (e.g. chain, tree, directed acyclic graph, general graph, …)?–Tree•(Re)memorize the environment model!a bcWrite the Scheme Code to Create the Following Environment DiagramGEWrite the Scheme Code to Create the Following Environment Diagrama bc(load "env-dia.scm")(define c (let ((a (let ((b nil)) (lambda (newb) (set! b newb) b)))) (a (lambda (x) (* x x)))))(env-dia 'render "tricky")GEOOPs•In the following code, how many references are created to the “anakin” symbol?(define (walker self name speed) (let ((named-part (named-object self name))) …))(define (biker self name speed) (let ((named-part (named-object self name))) …))(define (swimmer self name speed) (let ((named-part (named-object self name))) …))(define (tri-athlete self name walk-speed bike-speed swim-speed) (let ((walker-part (walker self name walk-speed)) (biker-part (biker self name bike-speed)) (swimmer-part (swimmer self name swim-speed))) …))(define (jedi self name) (let ((tri-athlete-part (tri-athelete self name 20 50 15))) …))(define anakin (create-jedi 'anakin))•8 (3 named-objects, walker, biker, swimmer, tri-athlete, jedi)–Moral: multiple personalities lead to Sithdom.Meandering Streams(define ones (cons-stream 1 ones))(define ints (cons-stream 1 (add-streams ones ints)))(define (row rnum col-stream) (if (null? col-stream) '() (cons-stream (list rnum (stream-car col-stream)) (row rnum (stream-cdr col-stream)))))(define (block started-rows next-row col-stream) (define (helper sr) (if (null? sr) (block (append (map stream-cdr started-rows) (list (row (stream-car next-row) col-stream))) (stream-cdr next-row) col-stream) (cons-stream (stream-car (car sr)) (helper (cdr sr))))) (helper (reverse started-rows)))(show-stream (block nil ints ints) 15)1 2 3 4 …1 (1 1) (1 2) (1 3) (1 4) …2 (2 1) (2 2) (2 3) (2 4) …3 (3 1) (3 2) (3 3) (3 4) …4 (4 1) (4 2) (4 3) (4 4) …… … … … … …What gets displayed by show-stream?(1 1) (2 1) (1 2) (3 1) (2 2) (1 3) (4 1) (3 2) (2 3) (1 4) (5 1) (4 2) (3 3) (2 4) (1 5)•What are the possible values for z at the completion of the parallel-execution below?(define z 5)(define (P1) (set! z (+ z 10)))(define (P2) (set! z (* z 2)))(parallel-execute P1 P2)Fall 1998 Exam: InterleavingsFall 1998 Exam: Interleavings (+ z 10))(set! z (* z 2)) (set! z 30 (+ z 10)) (* z 2))(set! z (set! z 10 (+ z 10)) (* z 2)) (set! z(set! z 15 (* z 2)) (+ z 10))(set! z (set! z 10 (* z 2)) (+ z 10)) (set! z(set! z 15 (* z 2)) (set! z (+ z 10))(set! z 20foreach special form(foreach var exp body-exp body-exp)(foreach x (list 1 2 3 4 5) (display x) (display " "))(define foreach-variable second)(define foreach-list third)(define foreach-body cdddr)(define (desugar-foreach exp) `(let loop ((lst ,(foreach-list exp))) (if (null? lst) #f (let ((,(foreach-variable exp) (car lst))) ,@(foreach-body exp) (loop (cdr lst))))))foreach special form(foreach var exp body-exp body-exp)(foreach x (list 1 2 3 4 5) (display x) (display " "))(define foreach-variable second)(define foreach-list third)(define foreach-body cdddr)(define (eval-foreach exp env) (let loop ((lst (foreach-list exp))) (if (null? lst) #f (begin (m-eval `(let ((,(foreach-variable exp) ,(car lst))) ,@(foreach-body exp)) env) (loop (cdr lst))))))foreach special form(foreach var exp body-exp body-exp)(foreach x (list 1 2 3 4 5) (display x) (display " "))(define foreach-variable second)(define foreach-list third)(define foreach-body cdddr)(define (eval-foreach-nocapture exp env) (for-each (m-eval `(lambda (,(foreach-variable exp)) ,@(foreach-body exp)) env) (m-eval (foreach-list exp)
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