Safe Haskell	None
Language	Haskell2010

Distribution.Compat.Newtype

Description

Per Conor McBride, the Newtype typeclass represents the packing and unpacking of a newtype, and allows you to operatate under that newtype with functions such as ala.

Synopsis

class Newtype o n | n -> o where
ala :: (Newtype o n, Newtype o' n') => (o -> n) -> ((o -> n) -> b -> n') -> b -> o'
alaf :: (Newtype o n, Newtype o' n') => (o -> n) -> ((a -> n) -> b -> n') -> (a -> o) -> b -> o'
pack' :: Newtype o n => (o -> n) -> o -> n
unpack' :: Newtype o n => (o -> n) -> n -> o

Documentation

class Newtype o n | n -> o where #

The FunctionalDependencies version of Newtype type-class.

Since Cabal-3.0 class arguments are in a different order than in newtype package. This change is to allow usage with DeriveAnyClass (and DerivingStrategies, in GHC-8.2). Unfortunately one have to repeat inner type.

newtype New = New Old
  deriving anyclass (Newtype Old)

Another approach would be to use TypeFamilies (and possibly compute inner type using GHC.Generics), but we think FunctionalDependencies version gives cleaner type signatures.

Methods

pack :: o -> n #

pack :: Coercible o n => o -> n #

unpack :: n -> o #

unpack :: Coercible n o => n -> o #

Instances

Newtype String FilePathNT #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: String -> FilePathNT # unpack :: FilePathNT -> String #
Newtype String Token' #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: String -> Token' # unpack :: Token' -> String #
Newtype String Token #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: String -> Token # unpack :: Token -> String #
Newtype a (Product a) #
Instance details Defined in Distribution.Compat.Newtype Methods pack :: a -> Product a # unpack :: Product a -> a #
Newtype a (Sum a) #
Instance details Defined in Distribution.Compat.Newtype Methods pack :: a -> Sum a # unpack :: Sum a -> a #
Newtype a (Identity a) #
Instance details Defined in Distribution.Compat.Newtype Methods pack :: a -> Identity a # unpack :: Identity a -> a #
Newtype a (MQuoted a) #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: a -> MQuoted a # unpack :: MQuoted a -> a #
Newtype [a] (List sep wrapper a) #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: [a] -> List sep wrapper a # unpack :: List sep wrapper a -> [a] #
Newtype (Set a) (Set' sep wrapper a) #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: Set a -> Set' sep wrapper a # unpack :: Set' sep wrapper a -> Set a #
Newtype (Either Version VersionRange) SpecVersion #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: Either Version VersionRange -> SpecVersion # unpack :: SpecVersion -> Either Version VersionRange #
Newtype (Either License License) SpecLicense #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: Either License0 License -> SpecLicense # unpack :: SpecLicense -> Either License0 License #
Newtype (CompilerFlavor, VersionRange) TestedWith #
Instance details Defined in Distribution.Parsec.Newtypes Methods pack :: (CompilerFlavor, VersionRange) -> TestedWith # unpack :: TestedWith -> (CompilerFlavor, VersionRange) #
Newtype (a -> a) (Endo a) #
Instance details Defined in Distribution.Compat.Newtype Methods pack :: (a -> a) -> Endo a # unpack :: Endo a -> a -> a #

ala :: (Newtype o n, Newtype o' n') => (o -> n) -> ((o -> n) -> b -> n') -> b -> o' #

>>> ala Sum foldMap [1, 2, 3, 4 :: Int]
10

Note: the user supplied function for the newtype is ignored.

>>> ala (Sum . (+1)) foldMap [1, 2, 3, 4 :: Int]
10

alaf :: (Newtype o n, Newtype o' n') => (o -> n) -> ((a -> n) -> b -> n') -> (a -> o) -> b -> o' #

>>> alaf Sum foldMap length ["cabal", "install"]
12

Note: as with ala, the user supplied function for the newtype is ignored.

pack' :: Newtype o n => (o -> n) -> o -> n #

Variant of pack, which takes a phantom type.

unpack' :: Newtype o n => (o -> n) -> n -> o #

Variant of pack, which takes a phantom type.