PLQ #2Done on:   Tuesday, October 4th

Question 1 @ 2022-10-04 19:15

Which of following is sensible and is formatted properly WRT indentation?

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• 1
  (With 'y {Num 2}
          {Mul {Id 'y} {Num 3}})
• 2
  (With {y 2}
    {* y 3})
• 3
  {with {y 2}
    {* y 3}}
• 4
  (With 'y
        (Num 2)
        (Mul (Id 'y) (Num 3)))
• 5
  {with {x 2} {* y 3})}
• 6
  (With {y (Num 2)} (Mul (Id 'y) (Num 3)))
• 7
  (With 'y (Num 2) (Mul (Id 'y) (Num 3)))

Question 2 @ 2022-10-04 19:22

What would be the result of this expression using our (hack of a) lazy evaluation implementation?

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• 1
  1
• 2
  2
• 3
  A bad syntax error
• 4
  A runtime error
• 5
  A compilation error
• 6
  An unbound x error

Question 3 @ 2022-10-04 19:29

In WAE, we had this bit in our subst function:

If we replace the marked line with (subst bound-body from to) in subst below, what would we get?

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• 6
• 8
• 10
• Unbound X
• Unbound Y
• Bad Syntax
• Infinite loop

Question 4 @ 2022-10-04 19:37

Choose all options that explains the problem with the following definition of substitution in WAE?

Substitution definition: To substitute an identifier i in an expression e with an expression v, replace all instances of i that are not themselves binding instances, and that are not in any nested scope, with the expression v.

(Choose all of the correct answers)

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• 1

  There is nothing wrong with this.

• 2

  This fails to distinguish between the binding instance and the bound instance of i.

• 3

  It fails to replace any instance of i that is in any nested scope of j, where j is different from i.

• 4

  It fails to replace any instance of i that is not itself a binding instance and is free in e.