PLQ #2Done on:   Tuesday, September 28th

Question 1 @ 2021-09-28 19:01

What’s the problem with this function?

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• 1
  It has parsing and evaluation intermixed.
• 2
  It repeats code.
• 3
  The order of operations is ambiguous.
• 4
  Nothing is wrong with it.

Question 2 @ 2021-09-28 19:03

Which of the following BNF grammars are ambiguous?

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• 1
  <AE> = <num> | <AE> + <AE> | <AE> * <AE>
• 2
  <AE> = <num> | ( <AE> + <AE> ) | ( <AE> * <AE> )
• 3
  <AE> = <MUL> + <MUL>
  <MUL> = <num> | <MUL> * <MUL>
• 4
  <AE> = <num> | <ADD> | <MUL>
  <ADD> = <AE> + <AE>
  <MUL> = <AE> * <AE>

Question 3 @ 2021-09-28 19:05

How is a language based on this grammar going to evaluate the expressions?

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• 1
  Right-to-Left
• 2
  Left-to-Right
• 3
  L-to-R for + & -, R-to-L for * & /
• 4
  R-to-L for + & -, L-to-R for * & /
• 5
  Ambiguous so pretty much random

Question 4 @ 2021-09-28 19:07

What is the reason we’re using BNFs to specify our language(s)?

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• 1

  They’re a common simple way of specifying grammars.

• 2

  They’re easier to implement compilers for.

• 3

  They’re inherently compositional so they simplify the semantics.

• 4

  They turned out to be useful representations, as seen by the history of S-expressions in Lisp.

• 5

  No real reason.