1. Compilation Sequence PLLab, NTHU,Cs2403 Programming Languages

3. An Overview of Lex PLLab, NTHU,Cs2403 Programming Languages Lex C compiler a.out Lex source program lex.yy.c input lex.yy.c a.out tokens

6. Lex with Yacc Lex Yacc yylex() yyparse() Lex source (Lexical Rules) Yacc source (Grammar Rules) Input Parsed Input lex.yy.c y.tab.c return token call

7. Regular Expressions

14. Pattern Matching Primitives PLLab, NTHU,Cs2403 Programming Languages Metacharacter Matches . any character except newline newline * zero or more copies of the preceding expression + one or more copies of the preceding expression ? zero or one copy of the preceding expression ^ beginning of line / complement $ end of line a|b a or b (ab)+ one or more copies of ab (grouping) [ab] a or b a{3} 3 instances of a “ a+b” literal “ a+b ” (C escapes still work)

21. Review of Lex Predefined Variables Name Function char *yytext pointer to matched string int yyleng length of matched string FILE *yyin input stream pointer FILE *yyout output stream pointer int yylex(void) call to invoke lexer, returns token char* yymore(void) return the next token int yyless(int n) retain the first n characters in yytext int yywrap(void) wrapup, return 1 if done, 0 if not done ECHO write matched string REJECT go to the next alternative rule INITAL initial start condition BEGIN condition switch start condition

27. example Contd.. to do just that. The rule [0–9]+ recognizes strings of digits; atoi converts the digits to binary and stores the result in k. The operator % (remainder) is used to check whether k is divisible by 7; if it is, it is incremented by 3 as it is written out.