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package test
/** A trait for totally ordered data.
*/
trait Ordered[+a] {
/** Result of comparing `this' with operand `that'.
* returns `x' where
* x < 0 iff this < that
* x == 0 iff this == that
* x > 0 iff this > that
*/
def compareTo [b >: a <% Ordered[b]](that: b): Int
def < [b >: a <% Ordered[b]](that: b): Boolean = (this compareTo that) < 0
def > [b >: a <% Ordered[b]](that: b): Boolean = (this compareTo that) > 0
def <= [b >: a <% Ordered[b]](that: b): Boolean = (this compareTo that) <= 0
def >= [b >: a <% Ordered[b]](that: b): Boolean = (this compareTo that) >= 0
}
object O {
implicit def view1(x: String): Ordered[String] = new Ordered[String] {
def compareTo [b >: String <% Ordered[b]](y: b): Int = y match {
case y1: String => x compareTo y1
case _ => -(y compareTo x)
}
}
implicit def view2(x: Char): Ordered[Char] = new Ordered[Char] {
def compareTo [b >: Char <% Ordered[b]](y: b): Int = y match {
case y1: Char => x - y1
case _ => -(y compareTo x)
}
}
implicit def view3[a <% Ordered[a]](x: List[a]): Ordered[List[a]] =
new Ordered[List[a]] {
def compareTo [b >: List[a] <% Ordered[b]](y: b): Int = y match {
case y1: List[a1] => compareLists(x, y1.asInstanceOf[List[a]])
case _ => -(y compareTo x)
}
private def compareLists(xs: List[a], ys: List[a]): Int = {
if (xs.isEmpty && ys.isEmpty) 0
else if (xs.isEmpty) -1
else if (ys.isEmpty) 1
else {
val s = xs.head compareTo ys.head;
if (s != 0) s
else compareLists(xs.tail, ys.tail)
}
}
}
}
abstract class Tree[+a <% Ordered[a]] {
def insert[b >: a <% Ordered[b]](x: b): Tree[b]
def elements: List[a]
}
object Empty extends Tree[Nothing] {
def insert[b >: Nothing <% Ordered[b]](x: b): Tree[b] = new Node(x, Empty, Empty)
def elements: List[Nothing] = List()
}
class Node[a <% Ordered[a]](elem: a, l: Tree[a], r: Tree[a]) extends Tree[a] {
def insert[b >: a <% Ordered[b]](x: b): Tree[b] =
if (x == elem) this
else if (x < elem) new Node(elem, l insert x, r)
else new Node(elem, l, r insert x)
def elements: List[a] =
l.elements ::: List(elem) ::: r.elements
}
case class Str(elem: String) extends Ordered[Str] {
def compareTo[b >: Str <% Ordered[b]](that: b): Int = that match {
case that1: Str => this.elem compareTo that1.elem
case _ => -(that compareTo this)
}
}
object Test {
import O._
private def toCharList(s: String): List[Char] =
if (s.length() == 0) List()
else s.charAt(0) :: toCharList(s.substring(1))
def main(args: Array[String]) {
{
var t: Tree[String] = Empty
for (s <- args) {
t = t insert s
}
Console.println(t.elements)
}
{
var t: Tree[Str] = Empty
for (s <- args) {
t = t insert Str(s)
}
Console.println(t.elements)
}
{
var t: Tree[List[Char]] = Empty
for (s <- args) {
t = t insert toCharList(s)
}
Console.println(t.elements)
}
}
}
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