#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

const int MAX_PROGRAM_LENGTH = 38911;
// FILE* outfile; for compiler.
char* input;
char* token;
char delims[] = " \n\r\t";

void next_token()
{
    static int started = 0;
    if (! started) {
        token = strtok (input, delims);
        started = 1;
    }
    else {
        token = strtok (NULL, delims);
    }
    if (token == NULL) token = "EOF";
}

void error(char* nt)
{
    fprintf(stderr, "Error in %s at token '%s'\n", nt, token);
    exit(1);
}

bool Opnd ()
{
    if (! strcmp (token, "true")) {
        next_token();
        return true;
    }
    else if (! strcmp(token, "false")) {
        next_token();
        return false;
    }
    else error("Opnd");
}

bool Expr ()
{
    bool r1, r2;

    if (! strcmp(token,"or")) {
        next_token(); r1 = Expr(); r2 = Expr();
        return r1 || r2;
    }
    else if (! strcmp(token,"and")){
        next_token(); r1 = Expr(); r2 = Expr();
        return r1 && r2;
    }
    else if (! strcmp(token,"exor")){ 
        next_token(); r1 = Expr(); r2 = Expr();
        return (r1 || r2) && (! (r1 && r2));
    }
    else if (! strcmp(token,"not")) {
        next_token(); r1 = Expr();
        return !r1;
    }
    else return Opnd();
}

bool Start ()
{
    bool result;
    next_token();
    result = Expr();
    if (strcmp(token, "EOF")) {
        error("Start");
    }
    return result;
}

int main(void)
{
    int result;
    FILE* infile = fopen("in.truth", "r");
    input = malloc(MAX_PROGRAM_LENGTH);
    fgets(input, MAX_PROGRAM_LENGTH, infile);
    result = Start();
    fclose(infile);
    printf("Result: %s\n", result ? "true" : "false");
    return 0; 
}