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|
%{
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int yylex(void);
%}
%union {
int sum;
int mul;
int num;
}
%type <sum> A
%token <num> NUM
%left '+' '-'
%nonassoc '*'
%nonassoc UMIN
%%
S:
| S A { printf("-> %d\n", $2); }
;
A: NUM { $$ = $1; }
| A '+' A { $$ = $1 + $3; }
| A '-' A { $$ = $1 - $3; }
| A '*' A { $$ = $1 * $3; }
| '-' A %prec UMIN { $$ = -$2; }
| '(' A ')' { $$ = $2; }
;
%%
enum {
MaxLine = 1000,
};
char line[MaxLine], *p;
int
yyerror()
{
puts("oops");
}
int
yylex()
{
char c;
p += strspn(p, "\t ");
switch ((c=*p++)) {
case '+':
case '-':
case '*':
case '(':
case ')':
return c;
case 0:
case '\n':
p--;
return 0;
}
if (isdigit(c)) {
yylval.num = strtol(p-1, &p, 0);
return NUM;
}
puts("lex error!");
return 0;
}
int
main()
{
while ((p=fgets(line, MaxLine, stdin))) {
if (yyparse() < 0)
puts("parse error!");
}
return 0;
}
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