Working with the Unix OS

Development Tools
}
- This is processed by yacc into file called y.tab.c
C statements from between %{ and %}, if any
C statements from after second %%, if any
main() { ...; yyparse(), ...}
yylex(){ ... }
...
yyparse() ( parser, which calls yylex )
- Using lex and yacc
LEX
- Input to lex:
definitions
%%
rules
%%
user subroutines
lexical rules grammar rules
| |
lex
yacc
| |
input yylex yyparse parsed input
lex regular expressions
[a-z]*
any number of characters, including zero
[a-z]+
one or more characters
[A-Z][a-z][A-Za-zO-9]* all strings with leading character
| or
ab?c
optional – matches ac or abc
Example:
/*
$ lex scan.1 ==> lex.yy.c
*/
D [0-9]
E [DEde][-+]?{D}+
%%
{D}+ printf("integer");
(D)+"."{D}*({E})? | /* at least one digit before . */
(D)*"."{D}+({E})? | /* at least one digit after . */
{D}+{E}
printf("real");
%%
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