if (expressionLevel != 0) {
output.append('(');
}
expressionLevel++;
BinaryExpression be = (BinaryExpression) e;
printExpression(be.left).append(' ').append(be.operatorToString()).append(' ');
printExpression(be.right);
expressionLevel--;
if (expressionLevel != 0) {
output.append(')');
}