_Coroutine Format {
	char ch; // used for communication
	int g, b; // global because used in destructor
	void main() {
		for ( ;; ) { // for as many characters
			for ( g = 0; g < 5; g += 1 ) { // groups of 5 blocks
				for ( b = 0; b < 4; b += 1 ) { // blocks of 4 characters
					for ( ;; ) { // for newline characters
						suspend();
						if ( ch != '\n' ) break; // ignore newline
					}
//					cout << ch; // print character
				}
//				cout << " "; // print block separator
			}
//			cout << endl; // print group separator
		}
	}
  public:
	Format() { resume(); } // start coroutine
//	~Format() { if ( g != 0 | | b != 0 ) cout << endl; }
	void prt( char ch ) { Format::ch = ch; resume(); }
};

int main() {
	Format fmt;
	for ( long int i = 0; i < 1000000000; i += 1 )
		fmt.prt( 'a' );
}

// Local Variables: //
// tab-width: 4 //
// compile-command: "u++-work -O2 -nodebug Format.cc" //
// End: //