Data.Semigroup.Reducer

reducers-3.12.1: Semigroups, specialized containers and a general map/reduce framework

Copyright | (c) Edward Kmett 2009
License | BSD3
Maintainer | ekmett@gmail.com
Stability | experimental
Portability | non-portable (MPTCs)
Safe Haskell | Trustworthy
Language | Haskell98

Data.Semigroup.Reducer

Description

A `c`-`Reducer` is a `Semigroup` with a canonical mapping from `c` to the Semigroup.

Synopsis

- class Semigroup m => Reducer c m where
  - unit :: c -> m
  - snoc :: m -> c -> m
  - cons :: c -> m -> m
- foldMapReduce :: (Foldable f, Monoid m, Reducer e m) => (a -> e) -> f a -> m
- foldMapReduce1 :: (Foldable1 f, Reducer e m) => (a -> e) -> f a -> m
- foldReduce :: (Foldable f, Monoid m, Reducer e m) => f e -> m
- foldReduce1 :: (Foldable1 f, Reducer e m) => f e -> m
- pureUnit :: (Applicative f, Reducer c n) => c -> f n
- returnUnit :: (Monad m, Reducer c n) => c -> m n
- newtype Count = Count {
  - getCount :: Int
  }

# Documentation

class Semigroup m => Reducer c m where

This type may be best read infix. A `c `Reducer` m` is a `Semigroup` `m` that maps values of type `c` through `unit` to values of type `m`. A `c`-`Reducer` may also supply operations which tack-on another `c` to an existing `Monoid` `m` on the left or right. These specialized reductions may be more efficient in some scenarios and are used when appropriate by a `Generator`. The names `cons` and `snoc` work by analogy to the synonymous operations in the list monoid.

This class deliberately avoids functional-dependencies, so that () can be a `c`-Reducer for all `c`, and so many common reducers can work over multiple types, for instance, First and Last may reduce both `a` and `Maybe` `a`. Since a `Generator` has a fixed element type, the input to the reducer is generally known and extracting from the monoid usually is sufficient to fix the result type. Combinators are available for most scenarios where this is not the case, and the few remaining cases can be handled by using an explicit type annotation.

Minimal definition: `unit`

Minimal complete definition

unit

Methods

unit :: c -> m

Convert a value into a `Semigroup`

snoc :: m -> c -> m

Append a value to a `Semigroup` for use in left-to-right reduction

cons :: c -> m -> m

Prepend a value onto a `Semigroup` for use during right-to-left reduction

Instances

Reducer Bool All |
Reducer Bool Any |
Reducer Int IntSet |
Reducer c () |
Reducer a Count |
Monoid m => Reducer m (WrappedMonoid m) |
Ord a => Reducer a (Set a) |
Reducer a (Seq a) |
Reducer a (Last a) |
Reducer a (First a) |
Ord a => Reducer a (Max a) |
Ord a => Reducer a (Min a) |
Num a => Reducer a (Product a) |
Num a => Reducer a (Sum a) |
Semigroup a => Reducer a (Dual a) |
Reducer c [c] |
HasUnion f => Reducer f (Union f) |
Semigroup m => Reducer m (Self m) |
Measured v a => Reducer a (FingerTree v a) |
(Reducer c m, Reducer c n) => Reducer c (m, n) |
(Reducer c m, Reducer c n, Reducer c o) => Reducer c (m, n, o) |
(Reducer c m, Reducer c n, Reducer c o, Reducer c p) => Reducer c (m, n, o, p) |
Applicative f => Reducer (f a) (Traversal f) |
Monad f => Reducer (f a) (Action f) |
Apply f => Reducer (f a) (Trav f) |
Reducer (Maybe a) (Last a) |
Reducer (Maybe a) (First a) |
(Applicative f, Reducer c m) => Reducer (f c) (Ap f m) |
Alternative f => Reducer (f a) (Alternate f a) |
(Monad f, Reducer c m) => Reducer (f c) (Mon f m) |
MonadPlus f => Reducer (f a) (MonadSum f a) |
(HasUnionWith f, Semigroup m, Monoid m) => Reducer (f m) (UnionWith f m) |
(Apply f, Reducer c m) => Reducer (f c) (App f m) |
Alt f => Reducer (f a) (Alter f a) |
Reducer c m => Reducer (WithReducer m c) m |
Reducer (a -> a) (Endo a) |
Reducer (Int, v) (IntMap v) |
Ord k => Reducer (k, v) (Map k v) |

foldMapReduce :: (Foldable f, Monoid m, Reducer e m) => (a -> e) -> f a -> m

Apply a `Reducer` to a `Foldable` container, after mapping the contents into a suitable form for reduction.

foldMapReduce1 :: (Foldable1 f, Reducer e m) => (a -> e) -> f a -> m

foldReduce :: (Foldable f, Monoid m, Reducer e m) => f e -> m

Apply a `Reducer` to a `Foldable` mapping each element through `unit`

foldReduce1 :: (Foldable1 f, Reducer e m) => f e -> m

Apply a `Reducer` to a `Foldable1` mapping each element through `unit`

pureUnit :: (Applicative f, Reducer c n) => c -> f n

returnUnit :: (Monad m, Reducer c n) => c -> m n

newtype Count

Constructors

Count |
Fields getCount :: Int

Instances

Eq Count |
Data Count |
Ord Count |
Read Count |
Show Count |
Monoid Count |
Hashable Count |
Semigroup Count |
Reducer a Count |