Computer Science & IT 14 min read
Compiler Design: LL(1) vs LR Parsing, First & Follow Sets, and Code Optimization
Compiler construction mechanics tested in technical interviews and screening tests.
#Compilers#Parsing#LR(1)#LL(1)#First Follow#GATE CS
In-Depth Interview Questions & Model Solutions
Q1Compare Top-Down LL(1) parsers with Bottom-Up LR(0), SLR(1), LALR(1), and CLR(1) parsers in terms of expressive power.
Power hierarchy: LL(1) < LR(0) < SLR(1) < LALR(1) < CLR(1) / LR(1). LL(1) parses Left-to-right constructing Leftmost derivation with 1 lookahead token. It cannot parse left-recursive grammars and has smaller grammar coverage. LR parsers parse Left-to-right constructing Rightmost derivation in reverse (Shift-Reduce). LR(1) keeps specific lookahead tokens with each item, eliminating shift-reduce conflicts that plague SLR(1). LALR(1) merges LR(1) states with identical cores, drastically reducing table size while avoiding shift-reduce conflicts (though it can introduce reduce-reduce conflicts on non-LALR grammars).
Key Technical Takeaways:
- Yacc / Bison use LALR(1) due to compact table size and high expressiveness.
- Eliminating left recursion is required for LL(1) but not for LR parsers.
Technical Panel Interview Strategy Tips
- Practice calculating First and Follow sets for ambiguous grammar test cases.
These modules are prepared for self-study and interview revision. InterviewJobs.in is not responsible for variations in actual board questions. See our Disclaimer Policy.