class SyntaxAnalyseCond extends SyntaxAnalyse {

	public SyntaxAnalyseCond(String s) {
		super(s);
	}

	/**
	 *  prueft, ob naechstes Zeichen dem uebergebenen entspricht
	 */
	boolean nextIs(char c) {
		if (next == c) {
			scan();
			return true;
		} else
			return false;
	}
	
	/**
	 *  liefert aktuelle Position in expressionS
	 */
	int getPos() {
		return pos;
	}
	
	/**
	 *  setzt (zurueck) auf Position p
	 */
	void setPos(int p) {
		pos = p-1;
		scan();
	}
	
	/**
	 *  prueft auf Condition
	 */
	boolean isCondition() {
		int pos = getPos();
		if (isExpression() && nextIs('=') && isExpression()) {
			if(DEBUG)System.out.println(" Condition recognized!");
			return true;
		} else {
			setPos(pos);
			if (nextIs('(') && isCondition() && nextIs(')')) {
				if(DEBUG)System.out.println(" '(' Condition ')' recognized!");
				return true;
			} else
				return false;
		}
	}
		
	/**
	 *  prueft auf Term (mit Condition)
	 */
	public boolean isTerm() {
		if ( next=='(' ) {
			scan();
			int pos = getPos(); 
			if ( isExpression() && nextIs(')') ) {
				if(DEBUG)System.out.println(" '(' Expression ')' recognized!");
				return true;
			} else {
				setPos(pos);
				return isCondition() && nextIs('/') && isExpression() 
				                     && nextIs('/') && isExpression() 
				                     && nextIs(')');
			}
		} else {
			return isAtom();
		}
	}
								   
	public static void main(String[] argv) {
		String inputString = "help";	
		java.io.BufferedReader keyboard =
			new java.io.BufferedReader(new java.io.InputStreamReader(System.in));
		while (!inputString.equals("exit")) {
			if (inputString.equals("help")) {
				System.out.println();			
				System.out.println(" Expression ::= Term                |");
				System.out.println("                Term '+' Expression |");
				System.out.println("                Term '-' Expression ");
				System.out.println("       Term ::= Atom                |");
				System.out.println("                '(' Expression ')'  |");
				System.out.println("                '(' Condition '/' Expression '/' Expression ')'");
				System.out.println("  Condition ::= Expression '=' Expression |");
				System.out.println("                '(' Condition ')'");
				System.out.println("       Atom ::= <a_number>");
			}
			System.out.print("\n\nType in your Expression, 'help' or 'exit': ");
			// read line from keyboard
			try {
				inputString = keyboard.readLine();
			}
			catch (java.io.IOException ioe) {
				System.out.println(" Error: "+ioe);				
			}
			if (inputString.equals("exit")) break;
			if (inputString.equals("help")) continue;
			if (inputString.length() == 0) continue;
			// syntax analyse 
			SyntaxAnalyseCond sa = new SyntaxAnalyseCond(inputString);
			if (sa.solve())
				System.out.println("\n\n RESULT: This is a VALID expression!");
			else
				System.out.println("\n\n RESULT: SYNTAX ERROR!");
		}
		System.out.println("Bye!");
	}

}