hashable-1.4.0.1: 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
License | BSD-3-Clause
Maintainer | johan.tibell@gmail.com
Stability | provisional
Portability | portable
Safe Haskell | Safe
Language | Haskell2010

Data.Hashable.Lifted

Contents

- Type Classes
- Auxiliary Functions
- Motivation

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

- class Eq1 t => Hashable1 t where
  - liftHashWithSalt :: (Int -> a -> Int) -> Int -> t a -> Int
- class Eq2 t => Hashable2 t where
  - liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> t a b -> Int
- hashWithSalt1 :: (Hashable1 f, Hashable a) => Int -> f a -> Int
- hashWithSalt2 :: (Hashable2 f, Hashable a, Hashable b) => Int -> f a b -> Int
- defaultLiftHashWithSalt :: (Hashable2 f, Hashable a) => (Int -> b -> Int) -> Int -> f a b -> Int

# Type Classes

class Eq1 t => 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 NonEmpty # | Since: 1.3.1.0
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> NonEmpty a -> Int #
Hashable1 IntMap # | Since: 1.3.4.0
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> IntMap a -> Int #
Hashable1 Tree # | Since: 1.3.4.0
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> Tree a -> Int #
Hashable1 Seq # | Since: 1.3.4.0
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> Seq a -> Int #
Hashable1 Set # | Since: 1.3.4.0
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> Set 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 (Proxy :: Type -> Type) # |
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> Proxy a -> Int #
Hashable k => Hashable1 (Map k) # | Since: 1.3.4.0
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> Map k 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 #
(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 #

class Eq2 t => 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 #
Hashable2 Map # | Since: 1.3.4.0
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt2 :: (Int -> a -> Int) -> (Int -> b -> Int) -> Int -> Map 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 #

# 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