type Any interface{}

type List interface {
	// IsNil returns true if the list is empty
	IsNil() bool

	// Cons returns a new list with val as the head
	Cons(val Any) List

	// Head returns the first element of the list;
	// panics if the list is empty
	Head() Any

	// Tail returns a list with all elements except the head;
	// panics if the list is empty
	Tail() List

	// Size returns the list's length.  This takes O(1) time.
	Size() int

	// ForEach executes a callback for each value in the list.
	ForEach(f func(Any))

	// Reverse returns a list whose elements are in the opposite order as
	// the original list.
	Reverse() List
}

type Map interface {
	// IsNil returns true if the Map is empty
	IsNil() bool

	// Set returns a new map in which key and value are associated.
	// If the key didn't exist before, it's created; otherwise, the
	// associated value is changed.
	// This operation is O(log N) in the number of keys.
	Set(key string, value Any) Map

	// Delete returns a new map with the association for key, if any, removed.
	// This operation is O(log N) in the number of keys.
	Delete(key string) Map

	// Lookup returns the value associated with a key, if any.  If the key
	// exists, the second return value is true; otherwise, false.
	// This operation is O(log N) in the number of keys.
	Lookup(key string) (Any, bool)

	// Size returns the number of key value pairs in the map.
	// This takes O(1) time.
	Size() int

	// ForEach executes a callback on each key value pair in the map.
	ForEach(f func(key string, val Any))

	// Keys returns a slice with all keys in this map.
	// This operation is O(N) in the number of keys.
	Keys() []string

	String() string
}