// 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 (sometimes called `Result`)

type Either[V any] interface {
	Maybe[V]
	Ok() bool
	Value() V
	Error() error
}

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

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

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

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

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

func (et *either[V]) Value() V {
	return et.value
}

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