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fn: fix and finish the either API

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This commit is contained in:
Keagan McClelland 2024-04-17 13:00:42 -06:00
parent c3603ccf96
commit 1dd56f1b2a
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GPG Key ID: FA7E65C951F12439
2 changed files with 106 additions and 7 deletions
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81
fn/either.go
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@ -16,6 +16,17 @@ func NewRight[L any, R any](r R) Either[L, R] {
return Either[L, R]{left: None[L](), right: Some(r)}
}
// ElimEither is the universal Either eliminator. It can be used to safely
// handle all possible values inside the Either by supplying two continuations,
// one for each side of the Either.
func ElimEither[L, R, O any](f func(L) O, g func(R) O, e Either[L, R]) O {
if e.left.IsSome() {
return f(e.left.some)
}
return g(e.right.some)
}
// WhenLeft executes the given function if the Either is left.
func (e Either[L, R]) WhenLeft(f func(L)) {
e.left.WhenSome(f)
@ -36,13 +47,69 @@ func (e Either[L, R]) IsRight() bool {
return e.right.IsSome()
}
// MapLeft maps the left value of the Either to a new value.
func MapLeft[L any, R any, O any](f func(L) O) func(Either[L, R]) Option[O] {
return func(e Either[L, R]) Option[O] {
if e.IsLeft() {
return MapOption(f)(e.left)
}
// LeftToOption converts a Left value to an Option, returning None if the inner
// Either value is a Right value.
func (e Either[L, R]) LeftToOption() Option[L] {
return e.left
}
return None[O]()
// RightToOption converts a Right value to an Option, returning None if the
// inner Either value is a Left value.
func (e Either[L, R]) RightToOption() Option[R] {
return e.right
}
// UnwrapLeftOr will extract the Left value from the Either if it is present
// returning the supplied default if it is not.
func (e Either[L, R]) UnwrapLeftOr(l L) L {
return e.left.UnwrapOr(l)
}
// UnwrapRightOr will extract the Right value from the Either if it is present
// returning the supplied default if it is not.
func (e Either[L, R]) UnwrapRightOr(r R) R {
return e.right.UnwrapOr(r)
}
// Swap reverses the type argument order. This can be useful as an adapter
// between APIs.
func (e Either[L, R]) Swap() Either[R, L] {
return Either[R, L]{
left: e.right,
right: e.left,
}
}
// MapLeft maps the left value of the Either to a new value.
func MapLeft[L, R, O any](f func(L) O) func(Either[L, R]) Either[O, R] {
return func(e Either[L, R]) Either[O, R] {
if e.IsLeft() {
return Either[O, R]{
left: MapOption(f)(e.left),
right: None[R](),
}
}
return Either[O, R]{
left: None[O](),
right: e.right,
}
}
}
// MapRight maps the right value of the Either to a new value.
func MapRight[L, R, O any](f func(R) O) func(Either[L, R]) Either[L, O] {
return func(e Either[L, R]) Either[L, O] {
if e.IsRight() {
return Either[L, O]{
left: None[L](),
right: MapOption(f)(e.right),
}
}
return Either[L, O]{
left: e.left,
right: None[O](),
}
}
}

32
fn/option.go
View File

@ -213,3 +213,35 @@ func (o Option[A]) UnsafeFromSome() A {
}
panic("Option was None()")
}
// OptionToLeft can be used to convert an Option value into an Either, by
// providing the Right value that should be used if the Option value is None.
func OptionToLeft[O, L, R any](o Option[O], r R) Either[O, R] {
if o.IsSome() {
return Either[O, R]{
left: o,
right: None[R](),
}
}
return Either[O, R]{
left: None[O](),
right: Some(r),
}
}
// OptionToRight can be used to convert an Option value into an Either, by
// providing the Left value that should be used if the Option value is None.
func OptionToRight[O, L, R any](o Option[O], l L) Either[L, O] {
if o.IsSome() {
return Either[L, O]{
left: None[L](),
right: o,
}
}
return Either[L, O]{
left: Some(l),
right: None[O](),
}
}