Lab 11: Macros

• lab11.zip

Due at 11:59pm on Friday, 11/09/2018.

Lab Check-in 7 questions here.

Starter Files

Download lab11.zip. Inside the archive, you will find starter files for the questions in this lab, along with a copy of the Ok autograder.

Submission

By the end of this lab, you should have submitted the lab with python3 ok --submit. You may submit more than once before the deadline; only the final submission will be graded. Check that you have successfully submitted your code on okpy.org.

• To receive credit for this lab, you must complete Questions 1 through 2 in lab11.scm (Questions 2 and 3 on this page) and submit through Ok.

Q1: REPL

Sign up for checkoffs in your lab if you'd like to get credit for this week's checkoff.
Explain REPL. What are the different stages and what is done in each stage?

Q2: WWSD: Macros

One thing to keep in mind when doing this question, builtins get rendered as so

scm> +
#[+]
scm> list
#[list]

Use Ok to test your knowledge with the following "What Would Scheme Display?" questions:

python3 ok -q wwsd-macros -u

scm> (define-macro (f x) (car x))
______
f
scm> (f (2 3 4)) ; type SchemeError for error, or Nothing for nothing
______
2
scm> (f (+ 2 3))
______
#[+]
scm> (define x 2000)
______
x
scm> (f (x y z))
______
2000
scm> (f (list 2 3 4))
______
#[list]
scm> (f (quote (2 3 4)))
______
SchemeError
scm> (define quote 7000)
______
quote
scm> (f (quote (2 3 4)))
______
7000

Toggle Solution

scm> (define-macro (g x) (+ x 2))
______
g
scm> (g 2)
______
4
scm> (g (+ 2 3))
______
SchemeError

Toggle Solution

scm> (define-macro (if-else-5 condition consequent) `(if ,condition ,consequent 5))
______
if-else-5
scm> (if-else-5 #t 2)
______
2
scm> (if-else-5 #f 3)
______
5
scm> (if-else-5 #t (/ 1 0))
______
SchemeError
scm> (if-else-5 #f (/ 1 0))
______
5
scm> (if-else-5 (= 1 1) 2)
______
2

Toggle Solution

Q3: Scheme def

Implement def, which simulates a python def statement, allowing you to write code like (def f(x y) (+ x y)).

Hint: the previous is equivalent to (def f (x y) (+ x y)).

Additional hint: use lambda in your solution.

(define-macro (def func bindings body)
    'YOUR-CODE-HERE
    `(define ,func (lambda ,bindings ,body))
)

Toggle Solution

Use Ok to test your code:

python3 ok -q scheme-def