Ceylon: Optional types

	/**
	In case you haven't heard of optional types you might
	want to take your profession more seriously :)
	Yes, i'm referring to constructs like Scala's algebraic type called Option
	which is either a Some(T value) or a None
	Ceylon does not use a wrapper class but instead makes use of 2 new cool
	features which are baked into the language "Union and Intersection Types"
	together with type narrowing.
	So if you want to express that a value can be either of the declared type or
	null, you use the syntactic sugar notation (appending a question mark)
	In order to be able to call methods on an union type, you first have to narrow it down
	to a specific type. In this case we do this by testing for existence.
	**/
	class Person(fName, middleName, lName) {
	shared String fName;
	shared String? middleName; //optional
	shared String lName;
	shared actual String string {
	//below we narrow the type to String
	if (exists middleName) {
	return "(Person(``fName`` ``middleName`` ``lName``))";
	}
	return "(Person(``fName`` ``lName``))";
	}
	}
	/**
	We can however use the else construct to provide a default value if the optional type
	is indeed null. This saves a few lines of code and might be even clearer.
	**/
	class Person2(fName, middleName, lName) {
	shared String fName;
	shared String? middleName; //optional
	shared String lName;
	shared actual String string => "(Person(``fName`` ``middleName else ""`` ``lName``))";
	}

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	/**
	This demo prints
	5
	<null>
	**/
	void optional_demo() {
	//Below we use syntactic sugar notation for optional type which basically is
	//the union of types Integer and Null
	Integer? optional1 = getNumber("robby");
	//Below we use the fully qualified union type
	Integer | Null optional2 = getNumber("john");
	print(optional1);
	print(optional2);
	}
	Integer? getNumber(String name) {
	return name.startsWith("r") then 5; //else null is implicit
	}

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