Question 1 @ 2024-02-13 18:28

Assuming a correct FLANG substitution, what will the following substitution result in?

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• A

  {call {fun {3} {+ 3 1}} {+ x 2}}

• B

  {call {fun {x} {+ 3 1}} {+ 3 2}}

• C

  {call {fun {x} {+ x 1}} {+ 3 2}}

• D

  {call {fun {x} {+ x 1}} {+ x 2}}

• E

  {call {fun {x} {+ x 1}} 5}

• F

  {call {fun {x} 4} 5}

• G

  Depends on the dynamic context that the expression gets evaluated in.

Question 2 @ 2024-02-13 18:32

In the properly dynamically scoped language that we discussed in class, what would the following code evaluate to?

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• -1 -1
• 1 1
• 2 2
• 3 3
• 5 5
• 7 7
• Imp Impossible to tell in a dynamically scoped language.

Question 3 @ 2024-02-13 18:36

In the properly dynamically scoped language that we discussed in class, what would the following code evaluate to?

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• 12 (1 2)
• 22 (2 2)
• 21 (2 1)
• 1122 (11 22)
• 2222 (22 22)
• 2211 (22 11)
• Imp Impossible to tell in a dynamically scoped language.

Question 4 @ 2024-02-13 18:39

What will the following return, assuming the current FLANG-ENV code in class?

(The Flang language, implemented with environments)

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• A (NumV 5) because that’s the value of x
• B (NumV 5) because eval always returns a NumV result
• C (FunV 'y (Add (Id 'y) (Id 'x)) (Extend 'x (NumV 5) (EmptyEnv)))
• D (FunV 'y (Add (Id 'y) (NumV 5)) (EmptyEnv))
• E The question is bogus because eval will throw an error on non-NumV results.

Question 5 @ 2024-02-13 18:44

Which of the following advantages of dynamic scope is correct?

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• A

  Dynamic scope facilitates easier compilation due to its reliance on the lexical structure of programs.

• B

  Dynamic scope allows for easy configuration of variables at runtime, making it good for languages like Racket.

• C

  Dynamic scope allows for easy configuration of variables at runtime, making it good for reusing code in unexpected ways.

• D

  Dynamic scope ensures that all functions are modifiable, leading to a more flexible codebase.

• E

  Dynamic scope makes recursion easy, but not as much as lexical scope.

Question 6 @ 2024-02-13 18:46

Reflecting on the Fun and Call expressions’ evaluation strategy, why is the substitution cache crucial for implementing closures in a language that supports first-class functions?

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• A

  It ensures that every function call is memoized, thus speeding up repeated calls to the same function with identical arguments.

• B

  It allows functions to retain access to the environment in which they were defined, independent of where they are called from dynamically.

• C

  It provides a mechanism for functions to modify their behavior dynamically based on the calling context.

• D

  It simplifies the parser implementation by caching parsed function bodies for reuse in subsequent evaluations.