PLQ #8Done on:   Tuesday, March 22nd

Question 1 @ 2022-03-22 18:51

In the new “Toy” language that we briefly discussed, what is the evaluation of the following snippet of code?

---

• a
  2
• b
  0
• c
  -2
• d
  Division by zero error
• e
  Syntax error
• f
  Runtime error

Question 2 @ 2022-03-22 18:59

Which of the following changes are made in the Toy language, relative to the Flang language?

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• 1
  There is no longer a need for a Call in the AST definition.
• 2
  A Frame is used to associate names and values in the environment.
• 3
  There is no longer a need for an extend function.
• 4
  The lookup function now requires a frame as one of its inputs.
• 5
  A FunV can now hold primitive Racket functions.

Question 3 @ 2022-03-22 19:02

Now that we have side effects including mutable boxes, we are able to implement objects with state. Which of the following is true about the object below?

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• 1
  Messages are analogous of methods.
• 2
  The xb value is essentially a “public” field.
• 3
  Object created with this make-counter are lexically scoped.
• 4
  set-box! is implemented as a chain of assignments, similar to C.
• 5
  The box call in the second line is analogous of inheritance.

Question 4 @ 2022-03-22 19:06

In our “OOP-like” example (repeated below), can we have recursive methods? What about “static members” — methods and variables?

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• 1
  None of these are possible, since they require inheritance.
• 2
  Recursive methods are possible, but static members require inheritance.
• 3
  Static members are possible, but recursive methods cannot be implemented since they need some “self” or “this” argument.
• 4
  Recursive methods and static variables are possible, but static methods require a “class scope” that we don’t have.
• 5
  All of these are possible.

Question 5 @ 2022-03-22 19:10

What is the main difference between a compiler and the curried TOY eval function?

---

• 1
  Nothing, they are semantically identical, just called differently.
• 2
  A real compiler would not be able to call itself recursively.
• 3
  The eval function requires a local helper, a compile would not.
• 4
  The eval function does not actually translate anything but a compiler does.
• 5
  A compiler would perform translation much faster than the eval function.