Explore the fundamental differences and concepts of LL(1) and LR(1) parsing algorithms with this quiz designed for computer science students and enthusiasts. Enhance your understanding of parsing techniques, table construction, and grammar compatibility in compiler design.
Which of the following parsing methods uses a single input symbol of lookahead and constructs a parse tree from the top down, such as in LL(1) parsing?
Explanation: LL(1) parsing operates top-down and looks one symbol ahead, enabling predictive parsing. Bottom-up methods like LR(1) parse from the leaves to the root, not the other way around. Having more than one lookahead or none at all does not characterize LL(1) parsers. Therefore, 'Top-down with one lookahead' captures the essence of the LL(1) approach.
Which type of context-free grammar can always be parsed by an LL(1) parser without backtracking?
Explanation: LL(1) requires grammars to be left-factored and free from left recursion for parsing without backtracking. Ambiguous grammars and those with left recursion present issues for LL(1) parsing. Regular grammars are simpler and can be LL(1), but the question refers to context-free grammars more broadly, making left-factored and left-recursion-free the correct choice.
How does the size of the parsing table typically compare between LL(1) and LR(1) parsing algorithms?
Explanation: LR(1) tables often have many states due to considering item sets and lookahead, making them much larger than their LL(1) counterparts. LL(1) tables remain compact for suitable grammars. Both tables are not always the same in size, and ambiguous grammars are generally not handled by either. Thus, the correct answer is 'LR(1) tables are generally larger than LL(1)'.
In which direction does an LR(1) parser read the input string during parsing?
Explanation: LR(1) stands for Left-to-right input scanning with Rightmost derivation in reverse, so the parser reads input left to right. Right to left is incorrect for LR(1), random order does not apply in deterministic parsing, and alternating directions are not used. Therefore, 'Left to right' is the correct option.
Which parser type, LL(1) or LR(1), is able to handle a larger class of grammars, including some that are ambiguous?
Explanation: LR(1) parsers can handle a wider range of grammars, including all deterministic context-free grammars and some ambiguous ones with conflict resolution. LL(1) parsers are limited to a much smaller, unambiguous subset. The distractors suggesting both can do so or neither are inaccurate, making 'LR(1)' the correct choice.
Which parsing approach directly relies on the calculation of FIRST and FOLLOW sets to build its parsing table?
Explanation: LL(1) parsing tables are constructed using FIRST and FOLLOW sets to determine production entries. LR-based parsers use item sets and states rather than just these sets. CFG(1) is not a standard type, and SLR(1), while using FOLLOW in a sense, is not directly reliant in the same way as LL(1). Hence, 'LL(1)' is correct.
During parsing, which type of parser uses a stack to simulate the rightmost derivation in reverse?
Explanation: LR(1) parsers simulate rightmost derivation in reverse using a stack, enabling them to handle more complex grammars. LL(1) parsers use stacks but for leftmost derivations. LZ(1) refers to compression, not parsing, and NFA parsing deals with automata, not context-free grammars. Therefore, 'LR(1) parser' is correct.
Which parsing method, LL(1) or LR(1), typically provides better error detection and recovery for syntax errors?
Explanation: LR(1) parsers can detect syntax errors as soon as they occur due to precise state tracking, enabling better error handling. LL(1) error detection is less powerful due to conflicts and limited lookahead. The distractor stating equally is incorrect, and neither is also inaccurate since both can detect errors, but LR(1) is generally superior.
Given the grammar S → aSb | ε, which parser can handle this grammar in a single pass without grammar transformation?
Explanation: This grammar is right recursive and can be handled directly by LR(1) parsing, as LR(1) can manage a wider class of grammars without modification. LL(1) parsers may require grammar adjustments if FIRST and FOLLOW overlap for ε-productions. While both might handle some similar grammars, in general, 'LR(1)' is correct for direct handling.
A shift-reduce or reduce-reduce conflict in a parsing table is a characteristic problem of which parser type?
Explanation: Shift-reduce and reduce-reduce conflicts are classic issues in constructing LR(1) parsing tables, typically due to ambiguous or problematic grammars. LL(1) parsers experience different conflicts like multiple entries for a cell, not shift-reduce. The other distractors are not standard parsing algorithm names. Thus, 'LR(1)' is the correct answer.