#include <stdio.h>
#include "recdesc.h"

/* global variables */

int tok;
int tokval;

extern FILE *yyin;
extern int yylex();
extern char *yytext;

void start (void) {
  tok = yylex();
  tokval = atoi(yytext);
  /*  printf("Recognized %d\n", tok); */
}

void advance(void) {
  tok = yylex();
  tokval = atoi(yytext);
  /*   printf("Recognized %d\n", tok); */
}

void stop (void) {
  fclose(yyin);
}

void error(void) {
  printf("Error in token %4d\n", tok);
}

int eat(enum token t) {
  int cur_tokval;
  printf("Reading token %4d, expecting %4d\n", tok, t);
  cur_tokval = tokval;
  if (tok == t) advance(); else error();
  return cur_tokval;
}

/* Implementation of the grammar */


int E (void) { 
  int l, r;
  l = eat(NUM); eat(EQ); r = eat(NUM); 
  return (l == r);}

int S (void) { 
  int e, l, r;
  switch (tok) {
  case IF: eat(IF); e = E(); eat(THEN); l = S(); eat(ELSE); r = S();
    if (e) return l; else return r;
    break;
  case PRINT: eat(PRINT); return (eat(NUM));
    break;
  default: error();
  }
}

/* Main function */

int main (void) {

  int yylexres;

  start();
  printf("Evaluation yields %d\n", S());
  stop();

  return 0;
}