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| author | Georgi Lyubenov <georgi.lyubenov@tweag.io> | 2022-06-14 13:06:38 +0300 |
|---|---|---|
| committer | Georgi Lyubenov <georgi.lyubenov@tweag.io> | 2022-09-08 17:14:36 +0300 |
| commit | 77209ab32aee6f58504b303fdea2df69f5a71027 (patch) | |
| tree | 4115353be46d258f8b4245072dc84ce06c18f289 /libraries/base | |
| parent | 7918265d53db963bfd3dd529b1063fb844549733 (diff) | |
| download | haskell-77209ab32aee6f58504b303fdea2df69f5a71027.tar.gz | |
Export liftA2 from Prelude
Changes:
In order to be warning free and compatible, we hide Applicative(..)
from Prelude in a few places and instead import it directly from
Control.Applicative.
Please see the migration guide at
https://github.com/haskell/core-libraries-committee/blob/main/guides/export-lifta2-prelude.md
for more details.
This means that Applicative is now exported in its entirety from
Prelude.
Motivation:
This change is motivated by a few things:
* liftA2 is an often used function, even more so than (<*>) for some
people.
* When implementing Applicative, the compiler will prompt you for either
an implementation of (<*>) or of liftA2, but trying to use the latter
ends with an error, without further imports. This could be confusing
for newbies.
* For teaching, it is often times easier to introduce liftA2 first,
as it is a natural generalisation of fmap.
* This change seems to have been unanimously and enthusiastically
accepted by the CLC members, possibly indicating a lot of love for it.
* This change causes very limited breakage, see the linked issue below
for an investigation on this.
See https://github.com/haskell/core-libraries-committee/issues/50
for the surrounding discussion and more details.
Diffstat (limited to 'libraries/base')
| -rw-r--r-- | libraries/base/Data/Complex.hs | 1 | ||||
| -rw-r--r-- | libraries/base/Data/List/NonEmpty.hs | 2 | ||||
| -rw-r--r-- | libraries/base/Data/Semigroup.hs | 2 | ||||
| -rw-r--r-- | libraries/base/Prelude.hs | 2 |
4 files changed, 4 insertions, 3 deletions
diff --git a/libraries/base/Data/Complex.hs b/libraries/base/Data/Complex.hs index c9b8040f92..734b2fabf4 100644 --- a/libraries/base/Data/Complex.hs +++ b/libraries/base/Data/Complex.hs @@ -35,6 +35,7 @@ module Data.Complex ) where +import Prelude hiding (Applicative(..)) import GHC.Base (Applicative (..)) import GHC.Generics (Generic, Generic1) import GHC.Float (Floating(..)) diff --git a/libraries/base/Data/List/NonEmpty.hs b/libraries/base/Data/List/NonEmpty.hs index 03f631a2a7..6a31569bbb 100644 --- a/libraries/base/Data/List/NonEmpty.hs +++ b/libraries/base/Data/List/NonEmpty.hs @@ -102,7 +102,7 @@ import Prelude hiding (break, cycle, drop, dropWhile, last, length, map, repeat, reverse, scanl, scanl1, scanr, scanr1, span, splitAt, tail, take, takeWhile, - unzip, zip, zipWith, (!!)) + unzip, zip, zipWith, (!!), Applicative(..)) import qualified Prelude import Control.Applicative (Applicative (..), Alternative (many)) diff --git a/libraries/base/Data/Semigroup.hs b/libraries/base/Data/Semigroup.hs index 08040dfea8..256f2761fd 100644 --- a/libraries/base/Data/Semigroup.hs +++ b/libraries/base/Data/Semigroup.hs @@ -98,7 +98,7 @@ module Data.Semigroup ( , ArgMax ) where -import Prelude hiding (foldr1) +import Prelude hiding (foldr1, Applicative(..)) import GHC.Base (Semigroup(..)) diff --git a/libraries/base/Prelude.hs b/libraries/base/Prelude.hs index 2e21888abc..1309c0969d 100644 --- a/libraries/base/Prelude.hs +++ b/libraries/base/Prelude.hs @@ -73,7 +73,7 @@ module Prelude ( -- ** Monads and functors Functor(fmap, (<$)), (<$>), - Applicative(pure, (<*>), (*>), (<*)), + Applicative(pure, (<*>), (*>), (<*), liftA2), Monad((>>=), (>>), return), MonadFail(fail), mapM_, sequence_, (=<<), |