Copyright | (C) 2011-2015 Edward Kmett |
---|---|
License | BSD-style (see the file LICENSE) |
Maintainer | Edward Kmett <ekmett@gmail.com> |
Stability | provisional |
Portability | portable |
Safe Haskell | Trustworthy |
Language | Haskell98 |
In mathematics, a semigroup is an algebraic structure consisting of a set together with an associative binary operation. A semigroup generalizes a monoid in that there might not exist an identity element. It also (originally) generalized a group (a monoid with all inverses) to a type where every element did not have to have an inverse, thus the name semigroup.
The use of (<>)
in this module conflicts with an operator with the same
name that is being exported by Data.Monoid. However, this package
re-exports (most of) the contents of Data.Monoid, so to use semigroups
and monoids in the same package just
import Data.Semigroup
- class Semigroup a where
- stimesMonoid :: (Integral b, Monoid a) => b -> a -> a
- stimesIdempotent :: Integral b => b -> a -> a
- stimesIdempotentMonoid :: (Integral b, Monoid a) => b -> a -> a
- mtimesDefault :: (Integral b, Monoid a) => b -> a -> a
- newtype Min a = Min {
- getMin :: a
- newtype Max a = Max {
- getMax :: a
- newtype First a = First {
- getFirst :: a
- newtype Last a = Last {
- getLast :: a
- newtype WrappedMonoid m = WrapMonoid {
- unwrapMonoid :: m
- class Monoid a where
- newtype Dual a :: * -> * = Dual {
- getDual :: a
- newtype Endo a :: * -> * = Endo {
- appEndo :: a -> a
- newtype All :: * = All {}
- newtype Any :: * = Any {}
- newtype Sum a :: * -> * = Sum {
- getSum :: a
- newtype Product a :: * -> * = Product {
- getProduct :: a
- newtype Option a = Option {}
- option :: b -> (a -> b) -> Option a -> b
- diff :: Semigroup m => m -> Endo m
- cycle1 :: Semigroup m => m -> m
- data Arg a b = Arg a b
- type ArgMin a b = Min (Arg a b)
- type ArgMax a b = Max (Arg a b)
Documentation
class Semigroup a where Source
Nothing
(<>) :: a -> a -> a infixr 6 Source
An associative operation.
(a<>
b)<>
c = a<>
(b<>
c)
If a
is also a Monoid
we further require
(<>
) =mappend
sconcat :: NonEmpty a -> a Source
Reduce a non-empty list with <>
The default definition should be sufficient, but this can be overridden for efficiency.
stimes :: Integral b => b -> a -> a Source
Repeat a value n
times.
Given that this works on a Semigroup
it is allowed to fail if you request 0 or fewer
repetitions, and the default definition will do so.
By making this a member of the class, idempotent semigroups and monoids can upgrade this to execute in
O(1) by picking stimes = stimesIdempotent
or stimes = stimesIdempotentMonoid
respectively.
Since: 0.17
stimesMonoid :: (Integral b, Monoid a) => b -> a -> a Source
stimesIdempotent :: Integral b => b -> a -> a Source
stimesIdempotentMonoid :: (Integral b, Monoid a) => b -> a -> a Source
mtimesDefault :: (Integral b, Monoid a) => b -> a -> a Source
Semigroups
Monad Min Source | |
Functor Min Source | |
MonadFix Min Source | |
Applicative Min Source | |
Foldable Min Source | |
Traversable Min Source | |
Generic1 Min Source | |
Bounded a => Bounded (Min a) Source | |
Enum a => Enum (Min a) Source | |
Eq a => Eq (Min a) Source | |
Data a => Data (Min a) Source | |
Num a => Num (Min a) Source | |
Ord a => Ord (Min a) Source | |
Read a => Read (Min a) Source | |
Show a => Show (Min a) Source | |
Generic (Min a) Source | |
(Ord a, Bounded a) => Monoid (Min a) Source | |
NFData a => NFData (Min a) Source | |
Hashable a => Hashable (Min a) Source | |
Ord a => Semigroup (Min a) Source | |
type Rep1 Min Source | |
type Rep (Min a) Source |
Monad Max Source | |
Functor Max Source | |
MonadFix Max Source | |
Applicative Max Source | |
Foldable Max Source | |
Traversable Max Source | |
Generic1 Max Source | |
Bounded a => Bounded (Max a) Source | |
Enum a => Enum (Max a) Source | |
Eq a => Eq (Max a) Source | |
Data a => Data (Max a) Source | |
Num a => Num (Max a) Source | |
Ord a => Ord (Max a) Source | |
Read a => Read (Max a) Source | |
Show a => Show (Max a) Source | |
Generic (Max a) Source | |
(Ord a, Bounded a) => Monoid (Max a) Source | |
NFData a => NFData (Max a) Source | |
Hashable a => Hashable (Max a) Source | |
Ord a => Semigroup (Max a) Source | |
type Rep1 Max Source | |
type Rep (Max a) Source |
Monad First Source | |
Functor First Source | |
MonadFix First Source | |
Applicative First Source | |
Foldable First Source | |
Traversable First Source | |
Generic1 First Source | |
Bounded a => Bounded (First a) Source | |
Enum a => Enum (First a) Source | |
Eq a => Eq (First a) Source | |
Data a => Data (First a) Source | |
Ord a => Ord (First a) Source | |
Read a => Read (First a) Source | |
Show a => Show (First a) Source | |
Generic (First a) Source | |
NFData a => NFData (First a) Source | |
Hashable a => Hashable (First a) Source | |
Semigroup (First a) Source | |
type Rep1 First Source | |
type Rep (First a) Source |
Monad Last Source | |
Functor Last Source | |
MonadFix Last Source | |
Applicative Last Source | |
Foldable Last Source | |
Traversable Last Source | |
Generic1 Last Source | |
Bounded a => Bounded (Last a) Source | |
Enum a => Enum (Last a) Source | |
Eq a => Eq (Last a) Source | |
Data a => Data (Last a) Source | |
Ord a => Ord (Last a) Source | |
Read a => Read (Last a) Source | |
Show a => Show (Last a) Source | |
Generic (Last a) Source | |
NFData a => NFData (Last a) Source | |
Hashable a => Hashable (Last a) Source | |
Semigroup (Last a) Source | |
type Rep1 Last Source | |
type Rep (Last a) Source |
newtype WrappedMonoid m Source
Provide a Semigroup for an arbitrary Monoid.
WrapMonoid | |
|
Generic1 WrappedMonoid Source | |
Bounded a => Bounded (WrappedMonoid a) Source | |
Enum a => Enum (WrappedMonoid a) Source | |
Eq m => Eq (WrappedMonoid m) Source | |
Data m => Data (WrappedMonoid m) Source | |
Ord m => Ord (WrappedMonoid m) Source | |
Read m => Read (WrappedMonoid m) Source | |
Show m => Show (WrappedMonoid m) Source | |
Generic (WrappedMonoid m) Source | |
Monoid m => Monoid (WrappedMonoid m) Source | |
NFData m => NFData (WrappedMonoid m) Source | |
Hashable a => Hashable (WrappedMonoid a) Source | |
Monoid m => Semigroup (WrappedMonoid m) Source | |
type Rep1 WrappedMonoid Source | |
type Rep (WrappedMonoid m) Source |
Re-exported monoids from Data.Monoid
class Monoid a where
The class of monoids (types with an associative binary operation that has an identity). Instances should satisfy the following laws:
mappend mempty x = x
mappend x mempty = x
mappend x (mappend y z) = mappend (mappend x y) z
mconcat =
foldr
mappend mempty
The method names refer to the monoid of lists under concatenation, but there are many other instances.
Some types can be viewed as a monoid in more than one way,
e.g. both addition and multiplication on numbers.
In such cases we often define newtype
s and make those instances
of Monoid
, e.g. Sum
and Product
.
mempty :: a
Identity of mappend
mappend :: a -> a -> a
An associative operation
mconcat :: [a] -> a
Fold a list using the monoid.
For most types, the default definition for mconcat
will be
used, but the function is included in the class definition so
that an optimized version can be provided for specific types.
Monoid Ordering | |
Monoid () | |
Monoid All | |
Monoid Any | |
Monoid ByteString | |
Monoid ByteString | |
Monoid Builder | |
Monoid Builder | |
Monoid ShortByteString | |
Monoid IntSet | |
Monoid Builder | |
Monoid [a] | |
Ord a => Monoid (Max a) | |
Ord a => Monoid (Min a) | |
Monoid a => Monoid (Dual a) | |
Monoid (Endo a) | |
Num a => Monoid (Sum a) | |
Num a => Monoid (Product a) | |
Monoid (First a) | |
Monoid (Last a) | |
Monoid a => Monoid (Maybe a) | Lift a semigroup into |
Monoid (IntMap a) | |
Ord a => Monoid (Set a) | |
Monoid (Seq a) | |
(Hashable a, Eq a) => Monoid (HashSet a) | |
Semigroup a => Monoid (Option a) | |
Monoid m => Monoid (WrappedMonoid m) | |
(Ord a, Bounded a) => Monoid (Max a) | |
(Ord a, Bounded a) => Monoid (Min a) | |
Monoid b => Monoid (a -> b) | |
(Monoid a, Monoid b) => Monoid (a, b) | |
Monoid a => Monoid (Const a b) | |
Monoid (Proxy k s) | |
Ord k => Monoid (Map k v) | |
(Eq k, Hashable k) => Monoid (HashMap k v) | |
(Monoid a, Monoid b, Monoid c) => Monoid (a, b, c) | |
Alternative f => Monoid (Alt * f a) | |
Monoid a => Monoid (Tagged k s a) | |
(Monoid a, Monoid b, Monoid c, Monoid d) => Monoid (a, b, c, d) | |
(Monoid a, Monoid b, Monoid c, Monoid d, Monoid e) => Monoid (a, b, c, d, e) | |
newtype Dual a :: * -> *
Generic1 Dual | |
Bounded a => Bounded (Dual a) | |
Eq a => Eq (Dual a) | |
Ord a => Ord (Dual a) | |
Read a => Read (Dual a) | |
Show a => Show (Dual a) | |
Generic (Dual a) | |
Monoid a => Monoid (Dual a) | |
NFData a => NFData (Dual a) | Since: 1.4.0.0 |
Semigroup a => Semigroup (Dual a) Source | |
type Rep1 Dual = D1 D1Dual (C1 C1_0Dual (S1 S1_0_0Dual Par1)) | |
type Rep (Dual a) = D1 D1Dual (C1 C1_0Dual (S1 S1_0_0Dual (Rec0 a))) |
newtype Endo a :: * -> *
The monoid of endomorphisms under composition.
newtype Sum a :: * -> *
Monoid under addition.
Generic1 Sum | |
Bounded a => Bounded (Sum a) | |
Eq a => Eq (Sum a) | |
Num a => Num (Sum a) | |
Ord a => Ord (Sum a) | |
Read a => Read (Sum a) | |
Show a => Show (Sum a) | |
Generic (Sum a) | |
Num a => Monoid (Sum a) | |
NFData a => NFData (Sum a) | Since: 1.4.0.0 |
Num a => Semigroup (Sum a) Source | |
type Rep1 Sum = D1 D1Sum (C1 C1_0Sum (S1 S1_0_0Sum Par1)) | |
type Rep (Sum a) = D1 D1Sum (C1 C1_0Sum (S1 S1_0_0Sum (Rec0 a))) |
newtype Product a :: * -> *
Monoid under multiplication.
Product | |
|
Generic1 Product | |
Bounded a => Bounded (Product a) | |
Eq a => Eq (Product a) | |
Num a => Num (Product a) | |
Ord a => Ord (Product a) | |
Read a => Read (Product a) | |
Show a => Show (Product a) | |
Generic (Product a) | |
Num a => Monoid (Product a) | |
NFData a => NFData (Product a) | Since: 1.4.0.0 |
Num a => Semigroup (Product a) Source | |
type Rep1 Product = D1 D1Product (C1 C1_0Product (S1 S1_0_0Product Par1)) | |
type Rep (Product a) = D1 D1Product (C1 C1_0Product (S1 S1_0_0Product (Rec0 a))) |
A better monoid for Maybe
Option
is effectively Maybe
with a better instance of Monoid
, built off of an underlying Semigroup
instead of an underlying Monoid
.
Ideally, this type would not exist at all and we would just fix the Monoid
instance of Maybe
Monad Option Source | |
Functor Option Source | |
MonadFix Option Source | |
Applicative Option Source | |
Foldable Option Source | |
Traversable Option Source | |
Generic1 Option Source | |
Alternative Option Source | |
MonadPlus Option Source | |
Eq a => Eq (Option a) Source | |
Data a => Data (Option a) Source | |
Ord a => Ord (Option a) Source | |
Read a => Read (Option a) Source | |
Show a => Show (Option a) Source | |
Generic (Option a) Source | |
Semigroup a => Monoid (Option a) Source | |
NFData a => NFData (Option a) Source | |
Hashable a => Hashable (Option a) Source | |
Semigroup a => Semigroup (Option a) Source | |
type Rep1 Option Source | |
type Rep (Option a) Source |
Difference lists of a semigroup
ArgMin, ArgMax
Arg
isn't itself a Semigroup
in its own right, but it can be placed inside Min
and Max
to compute an arg min or arg max.
Arg a b |
Bifunctor Arg Source | |
Functor (Arg a) Source | |
Foldable (Arg a) Source | |
Traversable (Arg a) Source | |
Generic1 (Arg a) Source | |
Eq a => Eq (Arg a b) Source | |
(Data a, Data b) => Data (Arg a b) Source | |
Ord a => Ord (Arg a b) Source | |
(Read a, Read b) => Read (Arg a b) Source | |
(Show a, Show b) => Show (Arg a b) Source | |
Generic (Arg a b) Source | |
(NFData a, NFData b) => NFData (Arg a b) Source | |
(Hashable a, Hashable b) => Hashable (Arg a b) Source | |
type Rep1 (Arg a) Source | |
type Rep (Arg a b) Source |