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abstract class LIST[+T] {
def isEmpty: Boolean
def head: T
def tail: LIST[T]
def prepend [U >: T] (x: U): LIST[U] = new CONS(x, this)
def map[U](f: T => U): LIST[U] = if (isEmpty) NIL else tail.map(f).prepend(f(head))
}
object NIL extends LIST[Nothing] {
def isEmpty = true
def head = throw new Error
def tail = ???
}
class CONS[U](hd: U, tl: LIST[U]) extends LIST[U] {
def isEmpty = false
def head: U = hd
def tail = tl
}
object Inferred {
def foo[T](x: T): T = x
val x = foo(1)
val y = foo("abc")
def bar[U](xs: LIST[U]): LIST[U] = xs
val n = NIL
val nn = bar(NIL)
val ints: LIST[Int] = NIL prepend 1
val ints1 = NIL prepend 1 prepend 2
val a = if (1 == 0) NIL else ints
val n2 = scala.collection.immutable.Nil
val ss2: scala.collection.immutable.List[String] = "abc" :: n2
val ss3 = "abc" :: n2
def cl = ((x: Int) => x + 1)
val ints2 = ints map (_ + 1)
val ints3 = new CONS[Int](1, NIL)
val ints4 = new CONS(1, NIL)
}
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