// Code derived from Stroustrup's PPP2 book
// § 6.8.1 Implementing Token_stream
//  -and beginning on p 211

#include <iostream>
#include <stdexcept>
#include <string>

using namespace std;

void error(const char* s) { throw runtime_error(s); }

//------------------------------------------------------------------------------
class Token {
 public:
  Token(char ch) : kind{ch} {}

  Token(char ch, double val) : kind{ch}, value{val} {}

  char   kind  = '0';
  double value = 0.0;
};

//------------------------------------------------------------------------------
class Token_stream {
 public:
  Token_stream();  // make a Token_stream that reads from cin

  Token get();             // get a Token
  void  putback(Token t);  // put a Token back

 private:
  bool  full;    // is there a Token in the buffer?
  Token buffer;  // here is where we keep a Token put back using putback()
};

//------------------------------------------------------------------------------
Token_stream::Token_stream() : full{false}, buffer{0}  // no Token in buffer
{
}

//------------------------------------------------------------------------------
void Token_stream::putback(Token t)
{
  if (full)
    error("putback() into a full buffer");

  buffer = t;     // copy t to buffer
  full   = true;  // buffer is now full
}

//------------------------------------------------------------------------------
int main()
try {
  Token_stream ts;
  ts.putback(')');

} catch (exception& e) {
  cerr << e.what() << '\n';
  return 1;

} catch (...) {
  cerr << "exception \n";
  return 2;
}