PLQ #11Done on:   Tuesday, April 12th

Question 1 @ 2022-04-12 19:20

Which one of the following is NOT a side effect?

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• 1
  print
• 2
  format
• 3
  set-box!
• 4
  read-line
• 5
  error
• 6
  random

Question 2 @ 2022-04-12 19:23

Last week, and in the homework, we discussed implementing side effects in a lazy language. Say that we want to add the ability to read a line with a given prompt — we’ll want to extend the IO type

What should the ReadPrompt type be?

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• 1
  [ReadPrompt (IO -> IO)]
• 2
  [ReadPrompt (IO -> String)]
• 3
  [ReadPrompt (String String -> IO)]
• 4
  [ReadPrompt String (IO -> String)]
• 5
  [ReadPrompt String (String -> IO)]
• 6
  [ReadPrompt String String IO]
• 7
  [ReadPrompt String ReadLine]

Question 3 @ 2022-04-12 19:26

Which statement about the above definitions is the most accurate?

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• 1
  and-fun and and-macro are completely equivalent.
• 2
  Both versions evaluate and eagerly.
• 3
  and-fun is better since it’s a plain function (which is preferable when possible).
• 4
  and-macro uses a lazy evaluation strategy.
• 5
  and-fun does not work because it is a function.
• 6
  and-macro does not work because it is a macro.
• 7
  Calling and-fun produces a boolean value while and-macro returns a Sexpr.

Question 4 @ 2022-04-12 19:33

The following macro definition is an attempt to implement a runtime debugging utility:

How is it broken?

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• 1

  It’s not actually broken, but could just as well be implemented as a function.

• 2

  The first printout will never happen since it’s not quoted.

• 3

  The second printout will never happen since it’s quoted.

• 4

  The first printout will happen at the wrong time.

• 5

  The first printout will never happen since its not part of the return value.