A top down parser generates ____a) Rightmost Derivation b) Right most derivation in reverse c) Left most derivation d) Left most derivation in reverse

To determine what a top-down parser generates, it’s essential to understand the nature of parsing algorithms. A top-down parser builds the parse tree from the top (starting symbol) down to the leaves (terminals). This approach corresponds to the way expressions can be derived from a grammar.

Analysis

1. Definitions:

   • Rightmost Derivation: A derivation that replaces the rightmost non-terminal first.
   • Leftmost Derivation: A derivation that replaces the leftmost non-terminal first.

2. Top-Down Parsing:

   • A top-down parser generates the structure of the parse by beginning with the start symbol and applying production rules in a way that resembles a leftmost derivation.

Conclusion

Based on the nature of top-down parsing and its mechanism of replacing the leftmost non-terminal each time, a top-down parser generates:

Final Answer

c) Left most derivation