carcdr.groovy

// java.lang.Listにメソッドを追加する
List.metaClass.carcdr = {
    [delegate.head(), delegate.tail()]
}

assert [1, 2, 3].carcdr() == [1, [2, 3]]

{->
    def (car, cdr) = [1, 2, 3].carcdr()
    assert car == 1
    assert cdr == [2, 3]
}()

// ヘルパクラス(?)を追加する
class CarCdr {
    def head, tail
    CarCdr(List list) {
        head = list.head()
        tail = list.tail()
    }
    Object getAt(int index) {
        (index == 0) ? head : tail
    }
    String toString() {
        "$head : $tail"
    }
}
{->
    println([1, 2, 3] as CarCdr)

    def (car, cdr) = [1, 2, 3] as CarCdr
    assert car == 1
    assert cdr == [2, 3]
}()