Copyright	(C) 2015 Mark Andrus Roberts
License	BSD-style (see the file LICENSE)
Maintainer	Mark Andrus Roberts <markandrusroberts@gmail.com>
Stability	provisional
Safe Haskell	None
Language	Haskell2010

Data.Monoid.Last

Contents

Last
Last'

Description

Last' n is a generalization of the Last exported by Data.Monoid: whereas Data.Monoid.Last returns up to one value, Last' n returns up to n values.

Data.Monoid.Last    a ≡
            Last' 1 a ≡
            Last    a

This library also provides an API-compatible type synonym Last and function getLast allowing you to use it as a drop-in replacement.

Synopsis

`Last`

type Last a = Last' 1 a Source

A type isomorphic to Data.Monoid.Last

getLast :: Last a -> Maybe a Source

Get the last value of type a, if any.

>>> getLast (foldMap pure [])
Nothing

>>> getLast (foldMap pure [1,2,3,4])
Just 4

`Last'`

data Last' n a Source

A generalized version of Data.Monoid.Last

Instances

Functor (Last' n) Source
KnownNat n => Applicative (Last' n) Source
Foldable (Last' n) Source
Traversable (Last' n) Source
Generic1 (Last' n) Source
KnownNat n => Alternative (Last' n) Source
Eq a => Eq (Last' n a) Source
(Data a, Typeable Nat n) => Data (Last' n a) Source
Ord a => Ord (Last' n a) Source
Read a => Read (Last' n a) Source
Show a => Show (Last' n a) Source
KnownNat n => IsString (Last' n Char) Source
Generic (Last' n a) Source
KnownNat n => Monoid (Last' n a) Source
type Rep1 (Last' n) Source
type Rep (Last' n a) Source

getLast' :: Last' n a -> [a] Source

Get the last n values or fewer of type a.

>>> getLast' (foldMap pure [1,2,3,4] :: Last' 0 Int)
[]

>>> getLast' (foldMap pure [1,2,3,4] :: Last' 1 Int)
[4]

>>> getLast' (foldMap pure [1,2,3,4] :: Last' 2 Int)
[3,4]