Question 1 @ 2024-03-26 18:23

Which of the following tools did we use to implement our lazy language?

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• A Thunks
• B Generators
• C Macros
• D Expression closures
• E Tail call optimization
• F Conditional evaluation

Question 2 @ 2024-03-26 18:28

If the following code is executed in our Lazy Racket language, what is the result? (In this example «E₁» and «E₂» are placeholders for some expression.)

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• A 11
• B 12
• C An error; the program crashes with a division by zero
• D An error; the program crashes because a list is given as the condition of ‘if’
• E Cannot answer this without knowing what is «E₁».
• F Cannot answer this without knowing what is «E₂».

Question 3 @ 2024-03-26 18:33

What problem in our Sloth implementation does the strict function solve?

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• A It allows constructing infinite lists.
• B It enables infinite loops.
• C It ensures that only RktVs are returned from the eval* function.
• D It handles cases where evaluating an ExprV results in an ExprV.
• E It creates a new closure of an ExprV and a given environment.
• F Strict does not solve any particular problem, it makes the code run more efficiently.
• G Strict does not solve any particular problem, it’s just a convenience function.

Question 4 @ 2024-03-26 18:36

As we’ve seen last week, generators and channels give programmers more expressive control flow constructs. Which of the following statements explains why this works?

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• A They use call-by-reference to delay evaluation.
• B They can be used to implement control flows that are different from the standard call-a-function-and-get-an-answer.
• C They provide a better implementation of short-circuit evaluations.
• D They are eagerly evaluated when called.
• E They cannot be partially evaluated.

Question 5 @ 2024-03-26 18:38

Consider the following type definition for VAL from our lazy Sloth evaluator:

Is this from the version of Sloth that implements a call by name or call by need language?

Choose the best answer.

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• A

  Call by name, because we look up the value of each ExprV in the environment using its name.

• B

  Call by name, because the value of each ExprV is recalculated every time it is evaluated.

• C

  Call by need, because the value of each ExprV is cached after the first time it is evaluated.

• D

  Call by need, because strict is only called on an ExprV when we need to force it into a proper value.

• E

  Impossible to tell, since the type definition is the same for both, only the implementation is different.