PLQ #5Done on:   Tuesday, February 22nd

Question 1 @ 2022-02-22 18:34

Consider the following FLANG test:

If this test succeeds, which kind of scope is it using?

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• 1
  Dynamic scope
• 2
  Global scope
• 3
  Lexical scope
• 4
  Function scope
• 5
  Impossible to tell

Question 2 @ 2022-02-22 18:37

Examine the following code block in the context of the dynamically-scoped version of FLANG. What does it evaluate to?

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• 101
• 11
• 2
• Unbound x
• Unbound y
• Unbound f
• Bad syntax

Question 3 @ 2022-02-22 18:41

Which of the following is true about substitution caches?

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• 1

  The FLANG implementation with substitution caches features lexical scoping rather than the dynamic scoping of the previous substitution based FLANG interpreter.

• 2

  The subst function remains unchanged once the lookup and extend functions are in place.

• 3

  The formal rules for cached substitutions remains unchanged from the previous FLANG eval formal spec.

• 4

  Evaluation by substitution is efficient because the AST is copied at each scope.

• 5

  None of the above.

Question 4 @ 2022-02-22 18:43

What are the possible use cases for dynamic scoping?

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• 1

  Allows for curried functions.

• 2

  Controlled dynamic-scope allows flexibility in customizing programs.

• 3

  Changing the semantics of a program.

• 4

  Enables efficient compilation.

• 5

  Simplifies reasoning about code.

• 6

  Recursion is immediately available.