| 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
- class Semigroup m => Reducer c m where
- 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 {}
Documentation
class Semigroup m => Reducer c m where Source #
This type may be best read infix. A c is a Reducer mSemigroup 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
Methods
Convert a value into a Semigroup
Append a value to a Semigroup for use in left-to-right reduction
Prepend a value onto a Semigroup for use during right-to-left reduction
Instances
foldMapReduce1 :: (Foldable1 f, Reducer e m) => (a -> e) -> f a -> m Source #
foldReduce1 :: (Foldable1 f, Reducer e m) => f e -> m Source #
pureUnit :: (Applicative f, Reducer c n) => c -> f n Source #
returnUnit :: (Monad m, Reducer c n) => c -> m n Source #