CS 1723, Trace of Parser, Wed Nov 25 1998, Page 1runner% cat aritht.c/* arith0.c: simple parser -- no output * grammar: * P ---> E ’#’ * E ---> T {(’+’|’-’) T} * T ---> S {(’*’|’/’) S} * S ---> F ’^’ S | S * F ---> char | ’(’ E ’)’ */#include <stdio.h>#include <stdlib.h>#include <ctype.h>char next;void E(void);void T(void);void S(void);void F(void);void error(void);void scan(void);void enter(char);void leave(char);void spaces(int);int level = 0;void main(void){ scan(); E(); if (next != ’#’) error(); else printf("Successful parse\n");}void E(void){ enter(’E’); T(); while (next == ’+’ || next == ’-’) { scan(); T(); } leave(’E’);}void T(void){ enter(’T’); S(); while (next == ’*’ || next == ’/’) { scan(); S(); } leave(’T’);}void S(void){ enter(’S’); F(); if (next == ’^’) { scan(); S(); } leave(’S’);}void F(void){ enter(’F’); if (isalpha(next)) { scan(); } else if (next == ’(’) { scan(); E(); if (next == ’)’) scan(); else error(); } else { error(); } leave(’F’);}void scan(void){ while (isspace(next = getchar())) ;}void error(void){ printf("\n*** ERROR ***\n"); exit(1);}void enter(char name){ spaces(level++); printf("%c: Enter, \t", name); printf("Next == %c\n", next);}void leave(char name){ spaces(--level); printf("%c: Leave, \t", name); printf("Next == %c\n", next);CS 1723, Trace of Parser, Wed Nov 25 1998, Page 2}void spaces(int local_level){ while (local_level-- > 0) printf(" ");}runner% cc -o aritht aritht.crunner% arithta+b#E: Enter, Next == a T: Enter, Next == a S: Enter, Next == a F: Enter, Next == a F: Leave, Next == + S: Leave, Next == + T: Leave, Next == + T: Enter, Next == b S: Enter, Next == b F: Enter, Next == b F: Leave, Next == # S: Leave, Next == # T: Leave, Next == #E: Leave, Next == #Successful parserunner% arithta*(b+c)#E: Enter, Next == a T: Enter, Next == a S: Enter, Next == a F: Enter, Next == a F: Leave, Next == * S: Leave, Next == * S: Enter, Next == ( F: Enter, Next == ( E: Enter, Next == b T: Enter, Next == b S: Enter, Next == b F: Enter, Next == b F: Leave, Next == + S: Leave, Next == + T: Leave, Next == + T: Enter, Next == c S: Enter, Next == c F: Enter, Next == c F: Leave, Next == ) S: Leave, Next == ) T: Leave, Next == ) E: Leave, Next == ) F: Leave, Next == # S: Leave, Next == # T: Leave, Next == #E: Leave, Next == #Successful parserunner% arithta-b-c#E: Enter, Next == a T: Enter, Next == a S: Enter, Next == a F: Enter, Next == a F: Leave, Next == - S: Leave, Next == - T: Leave, Next == - T: Enter, Next == b S: Enter, Next == b F: Enter, Next == b F: Leave, Next == - S: Leave, Next == - T: Leave, Next == - T: Enter, Next == c S: Enter, Next == c F: Enter, Next == c F: Leave, Next == # S: Leave, Next == # T: Leave, Next == #E: Leave, Next == #Successful parserunner% arithta^b^c#E: Enter, Next == a T: Enter, Next == a S: Enter, Next == a F: Enter, Next == a F: Leave, Next == ^ S: Enter, Next == b F: Enter, Next == b F: Leave, Next == ^ S: Enter, Next == c F: Enter, Next == c F: Leave, Next == # S: Leave, Next == # S: Leave, Next == # S: Leave, Next == # T: Leave, Next == #E: Leave, Next == #Successful