Type.Family.Either

Convenient type families for working with type-level Eithers.

Documentation

type family EitherC ec :: Constraint

Take a Maybe Constraint to a Constraint.

Equations

EitherC (Left a) = ØC

EitherC (Right c) = c

type family IsLeft a :: Bool

Equations

IsLeft (Left a) = True

IsLeft (Right b) = False

type family IsRight a :: Bool

Equations

IsRight (Left a) = False

IsRight (Right b) = True

leftCong :: (a ~ b) :- (IsLeft a ~ IsLeft b)

rightCong :: (a ~ b) :- (IsRight a ~ IsRight b)

leftNotRight :: (Left a ~ Right b) :- Fail

type family f <$> a :: Either m l infixr 4

Map over a type-level Maybe.

Equations

f <$> (Left a) = Left a

f <$> (Right b) = Right (f b)

eitherFmapCong :: (f ~ g, a ~ b) :- ((f <$> a) ~ (g <$> b))

type family f <&> a :: Either m l infixl 5

Equations

(Left x) <&> a = Left x

(Right f) <&> a = Right (f a)

eitherPamfCong :: (f ~ g, a ~ b) :- ((f <&> a) ~ (g <&> b))

type family f <*> a :: Either m l infixr 4

Equations

(Left x) <*> (Left y) = Left (x <> y)

(Left x) <*> a = Left x

f <*> (Left x) = Left x

(Right f) <*> (Right a) = Right (f a)

eitherApCong :: (f ~ g, a ~ b) :- ((f <*> a) ~ (g <*> b))

type family a <|> b :: Either m k infixr 4

Equations

(Left x) <|> b = b

(Right a) <|> b = Right a

eitherAltCong :: (a ~ c, b ~ d) :- ((a <|> b) ~ (c <|> d))

type family FromLeft e :: k

Equations

FromLeft (Left a) = a

type family FromRight e :: l

Equations

FromRight (Right b) = b

fromLeftCong :: (a ~ b) :- (FromLeft a ~ FromLeft b)

fromRightCong :: (a ~ b) :- (FromRight a ~ FromRight b)