PLQ #9

Question 1 @ 2022-03-29 18:35

As a reminder from last week, I was concerned that some of you do not have a complete understanding of what a closure is. Choose the TWO statements below that are correct.

1

Closures “close” over bindings which allows calling the functions in different contexts (different scopes).
2

Having closures ALWAYS means having lexical scope.
3

Local bindings are tied to the function CALL they’re at, and persist as long as the function call persists.
4

Local bindings are tied to the function VALUE they’re at, and persist as long as the function value persists.
5

A closure is synonymous with anonymous functions.

Question 2 @ 2022-03-29 18:55

In lecture last week, we started to build our TOY compiler. Which statement is FALSE about the discussion about refactoring our language evaluator into a compiler?

(define (compile expr)
(cases expr
[(Num n) (lambda ([env : ENV]) (RktV n))]
[(Id name) (lambda ([env : ENV]) (lookup name env))]
...))

1

We separated compile-time and run-time work.
2

Compilation is more efficient because it can reduce common expressions being evaluated over and over again.
3

Calls to compile should not happen at run-time.
4

Compilation is the result of performing a full evaluation.
5

It is only a “proper” compiler if its result has no references to the original code’s syntax (AST).

Question 3 @ 2022-03-29 19:00

If this is our code in the definitions window:

#lang pl lazy
(define l (append (list #f 2 (+ 3 "a")) l))

and then we enter the following on the REPL:

(or (first l) (fifth l))

what would we get?

1
Error, because one of the subexpressions will throw an error.
2
Error, because l is refers to itself.
3
Error, because l is bound to an infinite list.
4
A promise.
5
#f
6
2

Question 4 @ 2022-03-29 19:26

If the following code is run with lazy evaluation, which functions will get called?

(second (list (/ 2 0) (add1 2) (+ 1 3)))

(Note the multiple choice)

second
list
/
add1
+

Question 5 @ 2022-03-29 19:29

If the following code is run with eager evaluation, which functions will get called?