Describe two common idioms in context-free grammars that cannot be parsed top-down. 30. What is the “dangling else” problem? How is it avoided in modern languages? Discuss the similarities and...

Describe two common idioms in context-free grammars that cannot be parsed top-down. 30. What is the “dangling else” problem? How is it avoided in modern languages? Discuss the similarities and differences between recursive descent and tabledriven top-down parsing. What are FIRST and FOLLOW sets? What are they used for?