GATE CS 1992 Q02 — Parsing (LL, LR)

To compare the $\text{SLR(1)}$ and $\text{LALR(1)}$ parsing tables, we analyze their underlying state machines and construction rules:

1. State Machine Structure: Both $\text{SLR(1)}$ and $\text{LALR(1)}$ parsers are based on the same set of states as the $\text{LR(0)}$ parser. Since the states and the transitions between them are identical:
   • The goto transitions (on non-terminals) are identical in both tables. Thus, statement (A) is false.
   • The shift actions (transitions on terminals) are identical in both tables. Thus, statement (B) is true.
2. Reduce Actions:
   • In $\text{SLR(1)}$, for a state containing the item $A \to \alpha \cdot$, a reduce action is placed under all terminals in $\text{Follow}(A)$.
   • In $\text{LALR(1)}$, the reduce action is placed only under the specific lookahead terminals associated with that item in the merged $\text{LR(1)}$ state. Since these lookaheads are a subset of $\text{Follow}(A)$, the reduce entries can be different. Thus, statement (C) is true.
3. Error Entries: Since the reduce entries can differ between the two tables, the blank cells (which represent error entries) will also differ. Thus, statement (D) is true.

Therefore, the correct statements are B, C, and D.