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object lists {
abstract class List[a] {
def isEmpty: Boolean;
def head: a;
def tail: List[a];
def prepend(x: a) = Cons[a](x, this);
}
def Nil[b] = new List[b] {
def isEmpty: Boolean = true;
def head = sys.error("head of Nil");
def tail = sys.error("tail of Nil");
}
def Cons[c](x: c, xs: List[c]): List[c] = new List[c] {
def isEmpty = false;
def head = x;
def tail = xs;
}
def foo = {
val intnil = Nil[Int];
val intlist = intnil.prepend(1).prepend(1 + 1);
val x: Int = intlist.head;
val strnil = Nil[String];
val strlist = strnil.prepend("A").prepend("AA");
val y: String = strlist.head;
()
}
class IntList() extends List[Int] {
def isEmpty: Boolean = false;
def head: Int = 1;
def foo: List[Int] { def isEmpty: Boolean; def head: Int; def tail: List[Int] } = Nil[Int];
def tail0: List[Int] = foo.prepend(1).prepend(1 + 1);
def tail: List[Int] = Nil[Int].prepend(1).prepend(1 + 1);
}
def foo2 = {
val il1 = new IntList();
val il2 = il1.prepend(1).prepend(2);
()
}
}
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