While Loop using LR(1) Parser
This document presents the complete design and analysis of a WHILE loop construct using an
LR(1) parser as part of the Principles of Compiler Design (POCD) assignment.
1. Introduction
A parser is a core component of a compiler that checks the syntactic structure of source code.
LR(1) parsers are powerful bottom-up parsers that use one lookahead symbol and deterministic
parsing tables.
2. Grammar for While Loop
S → while_stmt while_stmt → WHILE ( C ) S | WHILE ( C ) { SL } SL → SL S | S C → E relop E
relop → < | > | <= | >= | == | != E → E + T | T T → T * F | F F → id | num
3. Augmented Grammar
S' → S
4. FIRST and FOLLOW Sets
FIRST(S) = { WHILE } FOLLOW(S) = { $ } FIRST(C) = { id, num } FOLLOW(C) = { ) }
5. Canonical LR(1) Items
The LR(1) item sets are constructed using closure and goto operations. Each state contains items
with lookahead symbols ensuring deterministic parsing.
6. LR(1) DFA
The DFA consists of states I0, I1, I2, ... representing canonical LR(1) item sets with transitions on
terminals and non-terminals.
7. ACTION and GOTO Table
ACTION table defines shift, reduce, and accept actions. GOTO table handles transitions for
non-terminals. Together they guide the LR(1) parsing process.
8. Parsing Example
Input: while ( id < num ) id = num ; Stack and input are processed step-by-step using ACTION and
GOTO tables until ACCEPT state is reached.
9. Conclusion
