hashable-1.3.0.0: A class for types that can be converted to a hash value
Copyright(c) Milan Straka 2010
(c) Johan Tibell 2011
(c) Bryan O'Sullivan 2011 2012
LicenseBSD-3-Clause
Maintainerjohan.tibell@gmail.com
Stabilityprovisional
Portabilityportable
Safe HaskellTrustworthy
LanguageHaskell2010

Data.Hashable.Lifted

Description

Lifting of the Hashable class to unary and binary type constructors. These classes are needed to express the constraints on arguments of types that are parameterized by type constructors. Fixed-point data types and monad transformers are such types.

Synopsis

Type Classes

class Hashable1 t where #

Minimal complete definition

Nothing

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> t a -> Int #

Lift a hashing function through the type constructor.

default liftHashWithSalt :: (Generic1 t, GHashable One (Rep1 t)) => (Int -> a -> Int) -> Int -> t a -> Int #

Instances

Instances details
Hashable1 [] # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> [a] -> Int #

Hashable1 Maybe # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Maybe a -> Int #

Hashable1 Complex # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Complex a -> Int #

Hashable1 Identity # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Identity a -> Int #

Hashable1 Hashed # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Hashed a -> Int #

Hashable a => Hashable1 (Either a) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a0 -> Int) -> Int -> Either a a0 -> Int #

Hashable a1 => Hashable1 ((,) a1) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> (a1, a) -> Int #

Hashable1 (Fixed :: Type -> Type) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Fixed a -> Int #

Hashable1 (Proxy :: Type -> Type) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Proxy a -> Int #

(Hashable a1, Hashable a2) => Hashable1 ((,,) a1 a2) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> (a1, a2, a) -> Int #

Hashable a => Hashable1 (Const a :: Type -> Type) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a0 -> Int) -> Int -> Const a a0 -> Int #

(Hashable a1, Hashable a2, Hashable a3) => Hashable1 ((,,,) a1 a2 a3) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> (a1, a2, a3, a) -> Int #

(Hashable1 f, Hashable1 g) => Hashable1 (Product f g) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Product f g a -> Int #

(Hashable1 f, Hashable1 g) => Hashable1 (Sum f g) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Sum f g a -> Int #

(Hashable a1, Hashable a2, Hashable a3, Hashable a4) => Hashable1 ((,,,,) a1 a2 a3 a4) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> (a1, a2, a3, a4, a) -> Int #

(Hashable1 f, Hashable1 g) => Hashable1 (Compose f g) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Compose f g a -> Int #

(Hashable a1, Hashable a2, Hashable a3, Hashable a4, Hashable a5) => Hashable1 ((,,,,,) a1 a2 a3 a4 a5) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> (a1, a2, a3, a4, a5, a) -> Int #

(Hashable a1, Hashable a2, Hashable a3, Hashable a4, Hashable a5, Hashable a6) => Hashable1 ((,,,,,,) a1 a2 a3 a4 a5 a6) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> (a1, a2, a3, a4, a5, a6, a) -> Int #

class Hashable2 t where #

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> t a b -> Int #

Lift a hashing function through the binary type constructor.

Instances

Instances details
Hashable2 Either # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> Either a b -> Int #

Hashable2 (,) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> (a, b) -> Int #

Hashable a1 => Hashable2 ((,,) a1) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> (a1, a, b) -> Int #

Hashable2 (Const :: Type -> Type -> Type) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> Const a b -> Int #

(Hashable a1, Hashable a2) => Hashable2 ((,,,) a1 a2) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> (a1, a2, a, b) -> Int #

(Hashable a1, Hashable a2, Hashable a3) => Hashable2 ((,,,,) a1 a2 a3) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> (a1, a2, a3, a, b) -> Int #

(Hashable a1, Hashable a2, Hashable a3, Hashable a4) => Hashable2 ((,,,,,) a1 a2 a3 a4) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> (a1, a2, a3, a4, a, b) -> Int #

(Hashable a1, Hashable a2, Hashable a3, Hashable a4, Hashable a5) => Hashable2 ((,,,,,,) a1 a2 a3 a4 a5) # 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> (a1, a2, a3, a4, a5, a, b) -> Int #

Auxiliary Functions

hashWithSalt1 :: (Hashable1 f, Hashable a) => Int -> f a -> Int #

Lift the hashWithSalt function through the type constructor.

hashWithSalt1 = liftHashWithSalt hashWithSalt

hashWithSalt2 :: (Hashable2 f, Hashable a, Hashable b) => Int -> f a b -> Int #

Lift the hashWithSalt function through the type constructor.

hashWithSalt2 = liftHashWithSalt2 hashWithSalt hashWithSalt

defaultLiftHashWithSalt :: (Hashable2 f, Hashable a) => (Int -> b -> Int) -> Int -> f a b -> Int #

Lift the hashWithSalt function halfway through the type constructor. This function makes a suitable default implementation of liftHashWithSalt, given that the type constructor t in question can unify with f a.

Motivation

This type classes provided in this module are used to express constraints on type constructors in a Haskell98-compatible fashion. As an example, consider the following two types (Note that these instances are not actually provided because hashable does not have transformers or free as a dependency):

newtype WriterT w m a = WriterT { runWriterT :: m (a, w) }
data Free f a = Pure a | Free (f (Free f a))

The Hashable1 instances for WriterT and Free could be written as:

instance (Hashable w, Hashable1 m) => Hashable1 (WriterT w m) where
    liftHashWithSalt h s (WriterT m) =
        liftHashWithSalt (liftHashWithSalt2 h hashWithSalt) s m
instance Hashable1 f => Hashable1 (Free f) where
    liftHashWithSalt h = go where
        go s x = case x of
            Pure a -> h s a
            Free p -> liftHashWithSalt go s p

The Hashable instances for these types can be trivially recovered with hashWithSalt1:

instance (Hashable w, Hashable1 m, Hashable a) => Hashable (WriterT w m a) where
    hashWithSalt = hashWithSalt1
instance (Hashable1 f, Hashable a) => Hashable (Free f a) where
    hashWithSalt = hashWithSalt1