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MyList.scala
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MyList.scala
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package com.anshu
abstract class MyList[+A] {
def head: A
def tail: MyList[A]
def isEmpty: Boolean
def add[B >: A](element: B): MyList[B]
def printElement: String
// polymorphic call
override def toString: String = "[" + printElement + "]"
def map[B](transformer: MyTransformer[A,B]): MyList[B]
def flatMap[B](transformer: MyTransformer[A, MyList[B]]): MyList[B]
def filter(predicate: MyPredicate[A]): MyList[A]
// concatenation
def ++[B >: A](list: MyList[B]): MyList[B]
}
object MyList{
def apply[A](values: A*) : MyList[A] = {
def buildList(valSeq: Seq[A], acc: MyList[A]): MyList[A] =
if (valSeq.isEmpty) acc
else buildList(valSeq.tail, acc add valSeq.head)
buildList(values.toSeq, Empty)
}
}
object Empty extends MyList[Nothing] {
def head: Nothing = throw new NoSuchElementException
def tail: MyList[Nothing] = throw new NoSuchElementException
def isEmpty: Boolean = true
def add[B >: Nothing](element: B): MyList[B] = new Cons(element, Empty)
def printElement: String = ""
def map[B](transformer: MyTransformer[Nothing,B]): MyList[B] = Empty
def flatMap[B](transformer: MyTransformer[Nothing, MyList[B]]): MyList[B] = Empty
def filter(predicate: MyPredicate[Nothing]): MyList[Nothing] = Empty
def ++[B >: Nothing](list: MyList[B]): MyList[B] = list
}
class Cons[+A](h: A, t: MyList[A]) extends MyList[A] {
def head: A = h
def tail: MyList[A] = t
def isEmpty: Boolean = false
def add[B >: A](element: B): MyList[B] = new Cons(element,this)
def printElement: String =
if (t.isEmpty) "" + h
else h + " " + t.printElement
def map[B](transformer: MyTransformer[A,B]): MyList[B] =
new Cons(transformer.transform(h), t.map(transformer))
def filter(predicate: MyPredicate[A]): MyList[A] =
if (predicate.test(h)) new Cons(h,t.filter(predicate))
else t.filter(predicate)
def ++[B >: A](list: MyList[B]): MyList[B] = new Cons(h, t ++ list)
def flatMap[B](transformer: MyTransformer[A, MyList[B]]): MyList[B] =
transformer.transform(h) ++ t.flatMap(transformer)
}
trait MyPredicate[-T] {
def test(elem: T): Boolean
}
trait MyTransformer[-A,B] {
def transform(elem: A): B
}
object ListTest extends App {
val list = new Cons(1, new Cons(2, Empty))
println(list.tail.head)
println(list.add(4).head)
println(list.isEmpty)
println(list.toString)
val listOfIntegers: MyList[Int] = new Cons(1,new Cons(2, new Cons(3, Empty)))
val anotherListOfIntegers: MyList[Int] = new Cons(4, new Cons(5, Empty))
val listOfStrings: MyList[String] = new Cons("Hello", new Cons("scala", Empty))
val listOfAny: MyList[Any] = new Cons(1, new Cons("hello", Empty))
println(listOfIntegers.toString)
println(listOfStrings.toString)
println(listOfAny.toString)
println(listOfIntegers.map(new MyTransformer[Int, Int] {
override def transform(elem: Int): Int = elem * 2
}).toString)
println(listOfIntegers.filter(new MyPredicate[Int] {
override def test(elem: Int): Boolean = elem % 2 == 0
}).toString)
println((listOfIntegers ++ anotherListOfIntegers).toString)
println((listOfIntegers.flatMap(new MyTransformer[Int, MyList[Int]] {
override def transform(elem: Int): MyList[Int] = new Cons(elem, new Cons(elem + 1, Empty))
})))
val lst = List(1,2,3,4,5)
println(lst.toString)
}