/* calc.l
   simple postfix calculator written in lex
   Daniel Scharstein 2/18/08
*/
%{
# include <stdio.h>
# include <stdlib.h>

void push(int n);
int pop();

int stack[1000];
int sp = 0;
%}

digit   [0-9]
num     -?{digit}+

%%

{num}   { push(atoi(yytext)); }
"+"     { push(pop() + pop()); }
"-"     { int a = pop(); push(pop() - a); }
"*"     { push(pop() * pop()); }
"/"     { int a = pop(); push(pop() / a); }
[ \t]   {}
"\n"    { printf("result=%d\n", pop()); }
.       { printf("syntax error\n"); }

%%

void push(int n) {
  stack[++sp] = n;
}

int pop() {
  return stack[sp--];
}