GATE CS 2025 Set 1 Q.46: Parsing and Syntax Analysis (LL and LR)

Which of the following statement(s) is/are TRUE while computing First and Follow during top down parsing by a compiler?

For a production $A \to \epsilon$ , $\epsilon$ will be added to $\text{First}(A)$ .

If there is any input right end marker, it will be added to $\text{First}(S)$ , where $S$ is the start symbol.

For a production $A \to \epsilon$ , $\epsilon$ will be added to $\text{Follow}(A)$ .

If there is any input right end marker, it will be added to $\text{Follow}(S)$ , where $S$ is the start symbol.

Official answer and solution

Solution

Recall the standard rules for constructing $\text{First}$ and $\text{Follow}$ sets in LL(1) parsing.

By the rules for computing $\text{First}$ and $\text{Follow}$ sets:

(A) True: If $A \to \epsilon$ is a production, then $\epsilon \in \text{First}(A)$ .
(B) False: The input right end-marker ($) is never placed in $\text{First}$ sets.
(C) False: $\text{Follow}$ sets contain only terminals and the end-marker $; $\epsilon$ is never in any $\text{Follow}$ set.
(D) True: The right end-marker $ is always added to $\text{Follow}(S)$ for the start symbol $S$ .

Final answer

Options (A), (D)

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Paper: GATE 2025 Computer Science and Information Technology - Session 1 (CS1)
Question: 46 of 65
Section: Computer Science and Information Technology

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