From b4f84e4bfac3648864d9482b7585a01d44b5eb58 Mon Sep 17 00:00:00 2001
From: James Henri Haydon <james.haydon@gmail.com>
Date: Fri, 28 Jul 2023 10:32:49 +0900
Subject: [PATCH] Explicit methods for Alternative Compose
Explicitly define some and many in Alternative instance for
Data.Functor.Compose
Implementation of https://github.com/haskell/core-libraries-committee/issues/181
---
libraries/base/changelog.md | 1 +
libraries/base/src/Data/Functor/Compose.hs | 4 ++++
2 files changed, 5 insertions(+)
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index 4d7d76ae4788..f2b04008bf4f 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -11,6 +11,7 @@
* Export List from Data.List ([CLC proposal #182](https://github.com/haskell/core-libraries-committee/issues/182)).
* Deprecate `Data.List.NonEmpty.unzip` ([CLC proposal #86](https://github.com/haskell/core-libraries-committee/issues/86))
* Fix exponent overflow/underflow bugs in the `Read` instances for `Float` and `Double` ([CLC proposal #192](https://github.com/haskell/core-libraries-committee/issues/192))
+ * Implement `many` and `some` methods of `instance Alternative (Compose f g)` explicitly. ([CLC proposal #181](https://github.com/haskell/core-libraries-committee/issues/181))
* The functions `GHC.Exts.dataToTag#` and `GHC.Base.getTag` have had
their types changed to the following:
diff --git a/libraries/base/src/Data/Functor/Compose.hs b/libraries/base/src/Data/Functor/Compose.hs
index ef2d305a7aab..2af347afdb8d 100644
--- a/libraries/base/src/Data/Functor/Compose.hs
+++ b/libraries/base/src/Data/Functor/Compose.hs
@@ -147,6 +147,10 @@ instance (Alternative f, Applicative g) => Alternative (Compose f g) where
empty = Compose empty
(<|>) = coerce ((<|>) :: f (g a) -> f (g a) -> f (g a))
:: forall a . Compose f g a -> Compose f g a -> Compose f g a
+ some = coerce (fmap sequenceA . some :: f (g a) -> f (g [a]))
+ :: forall a . Compose f g a -> Compose f g [a]
+ many = coerce (fmap sequenceA . many :: f (g a) -> f (g [a]))
+ :: forall a . Compose f g a -> Compose f g [a]
-- | The deduction (via generativity) that if @g x :~: g y@ then @x :~: y@.
--
--
GitLab