PLQ #4Done on:   Tuesday, February 16th

Question 1 @ 2021-02-16 18:21

What would we get if we run the following expression in our FLANG evaluator:

---

• 1

  We’d get 5.

• 2

  We’d get 6.

• 3

  We’d get an error because we cannot call functions with more than one argument.

• 4

  We’d get a bad syntax error, since we shouldn’t use call for arithmetic operators

• 5

  We’d get an error when trying to bind + since it’s a built-in.

• 6

  We’d get an error when trying to evaluate * since it’s free.

Question 2 @ 2021-02-16 18:26

Alice wants to map a curried version of the expt function onto a list of inputs. She first writes the function currify, which takes a two argument function and returns the curried version of the function.

She then writes a test using a curried expt function (Racket’s exponent):

What will be the result of this test?

---

• 1

  It will do whatever Racket does.

• 2

  It will pass, because (expt 2 3) evaluates to 8.

• 3

  It will fail, because the map will evaluate to a list of numbers, not a single number.

• 4

  It will error, because the function (currify expt) needs to be called on an input before it is passed into map.

• 5

  It will fail, because the map will evaluate to a list of one argument functions instead.

Question 3 @ 2021-02-16 18:29

If we drop with from our FLANG language, would we get a weaker language?

---

• 1
  No.
• 2
  Yes.
• 3
  No, because we can achieve the same using call and fun.
• 4
  Yes, because we will lose having functions too.
• 5
  Yes, because we will lose first-class functions.
• 6
  Yes, because the rule in the grammar will become useless too.
• 7
  Neither: we get a language that is just different.

Question 4 @ 2021-02-16 18:32

What is a good name for the following function?

---

• 1

  Trick question: this has free identifiers and therefore always an error.

• 2

  functional-addition

• 3

  compose

• 4

  compose-at-point

• 5

  reverse-compose

• 6

  reverse-compose-at-point