Ceylon: Range and Enumerable

	/**
	A quick look at the signature of Range reveals
	class Range<Element>
	extends Object() satisfies [Element+] & Cloneable<Range<Element>>
	given Element satisfies Ordinal<Element> & Comparable<Element>
	So in order to use a class in range notation we have to satisfy Ordinal & Comparable.
	Let's get started and come up with an example :)
	Oh yes... I used Enumerable which is a subtype of Ordinal.
	**/
	shared abstract class Priority(name, integerValue)
	of low | middle | high | critical
	satisfies Enumerable<Priority> & Comparable<Priority> {
	shared String name;
	shared actual Integer integerValue;
	shared actual Comparison compare(Priority other) => integerValue <=> other.integerValue;
	shared actual String string => name;
	}
	//ATTENTION !! You have to use the arrow notation for defining successor
	//and predecessor, meaning it is lazy evaluated because otherwise
	//you will run into a cyclic initialization error.
	shared object low extends Priority("minor", 1) {
	shared actual Priority predecessor => critical;
	shared actual Priority successor => middle;
	}
	shared object middle extends Priority("middle", 2) {
	shared actual Priority predecessor => low;
	shared actual Priority successor => high;
	}
	shared object high extends Priority("high", 3) {
	shared actual Priority predecessor => middle;
	shared actual Priority successor => critical;
	}
	shared object critical extends Priority("critical", 4) {
	shared actual Priority predecessor => high;
	shared actual Priority successor => low;
	}
	/**
	This prints
	**************prios for range middle..critical
	middle
	high
	critical
	**************prios for range critical..middle
	critical
	high
	middle
	**************prios for range high..minor
	high
	middle
	minor
	**/
	void range_demo() {
	printPrios(middle..critical);
	printPrios(critical..middle);
	printPrios(high..low);
	}
	void printPrios(Range<Priority> prios) {
	print("**************prios for range ``prios``");
	for (prio in prios) {
	print(prio);
	}
	}

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