/* flex file for lexical analyser for PLUS-TIMES-POWER expressions,
which involve simple arithmetic for nonnegative integers
with addition, multiplication and powers.
, Monash University
Initially, copied from the Wikipedia page for lex, then modified over time.
Last updated: 11 September 2021
*/
/*** Definition section ***/
%{
/* C code to be copied verbatim */
#include
#include
#include
void yyerror(char *);
#include “quat.h”
/*
#include “y.tab.h”
*/
%}
%%
/*** Rules section ***/
/* yytext is a string containing the matched text. */
/* Nonnegative integers … */
/* For QUAT, this regexp needs to be replaced by one for nonnegative reals. */
(0|[1-9][0-9]*) {
printf(“Token: NUMBER; Lexeme: %s\n”, yytext);
/*
yylval.num = atof(yytext);
return NUMBER;
*/
}
/* Next seven lines of code only relevant to QUAT and Problems 4-6. */
(ReplaceThisTextByRegexpForNonnegativeIntegers) {
printf(“Token: WHOLENUMBER; Lexeme: %s\n”, yytext);
/*
yylval.iValue = atoi(yytext);
return WHOLENUMBER;
*/
}
Power {
printf(“Token: POWER; Lexeme: %s\n”, yytext);
/*
yylval.str = strdup(yytext);
return POWER;
*/
}
[+*(),] {
printf(“Token and Lexeme: %s\n”, yytext);
/*
return *yytext;
*/
}
\n {
printf(“Token and Lexeme:
/*
return *yytext;
*/
}
[ \t] { } /* skip whitespace */
. {
printf(“Invalid character.\n”);
/*
yyerror(“invalid character”);
*/
}
/* will match any single character that does not match
any of the above patterns
*/
%%
/*** C Code section ***/
void yyerror(char *s) {
fprintf(stderr, “line %d: yytext = %s. Error msg: %s.\n”, yylineno, yytext, s);
}
int yywrap(void) {
return 1;
}
/* comment out the function main() if using lex with yacc */
int main(void) {
yylex();
return 0;
}