// Package funky provides a few constructs usually present in pure
// functional programming environments, using Go 1.18 generics.
package funky

// Maybe (sometimes called `Option`)

type Maybe[V any] interface {
	IsNothing() bool
	Value() V
}

type maybe[V any] struct {
	isNothing bool
	value     V
}

func Nothing[V any]() Maybe[V] {
	return &maybe[V]{isNothing: true}
}

func Just[V any](v V) Maybe[V] {
	return &maybe[V]{false, v}
}

func (m *maybe[V]) IsNothing() bool {
	return m.isNothing
}

func (m *maybe[V]) Value() V {
	return m.value
}

// Either

type Either[V any] interface {
	Ok() bool
	Right() V
	Left() error
}

type either[V any] struct {
	ok    bool
	right V
	left  error
}

func Right[V any](v V) Either[V] {
	return &either[V]{
		ok:    true,
		right: v,
	}
}

func Left[V any](e error) Either[V] {
	return &either[V]{left: e}
}

func (et *either[V]) Ok() bool {
	return et.ok
}

func (et *either[V]) Right() V {
	return et.right
}

func (et *either[V]) Left() error {
	return et.left
}