- https://stackoverflow.com/questions/5975741/what-is-the-difference-between-ll-and-lr-parsing
- https://web.stanford.edu/class/archive/cs/cs143/cs143.1128/
- https://www.joinc.co.kr/w/Site/Development/Env/Yacc
- Lexical analysis (lex, flex, ...)
- Reads the source code, and generates tokens
- Each token may have attributes - property like int
- Regular expression will be converted to NFA then DFA
- Syntax analysis (yacc, bison, ...)
- Or parsing
- Build structure using tokens
- Report errors encoding structures
- Top down vs Bottom up
- Semantic analysis
- IR generation
- IR optimization
- Code generation
- Optimization
- TOP Down (LL)
- Begins with just the start symbol
- Need to guess
- Bottom-up (LR)
- Has an extension of *.l (elle), as from lex
%{
/* Defintion section
- Variable declaration
- header file here
*/
%}
%%
/* Rules section
Pattern action
*/
%%
/*
User code may be here
*/
- Has an extension of *.y, as from yacc
%{
/* C declaration
- Variable declaration
- header file here
*/
%}
// Bison declaration
%%
/* Bison grammar
Pattern action
*/
%%
/*
User code may be here
*/
- flex is for Lexical analysis
- Ex: Number or word
- Save as ex2.l
%{
#include <stdio.h>
%}
%%
[0123456789]+ printf("NUMBER\n");
[a-zA-Z][a-zA-Z0-9]* printf("WORD\n");
%%
- Compile as `flex ex2.l; gcc lex.yy.c -o ex2 -lfl`
$ ./ex2
abc
WORD
123
NUMBER
abc 123
WORD
NUMBER
ctr+D
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