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| -rw-r--r-- | libraries/base/Data/Semigroup.hs | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/libraries/base/Data/Semigroup.hs b/libraries/base/Data/Semigroup.hs index 918351f62e..9a21b9a2ec 100644 --- a/libraries/base/Data/Semigroup.hs +++ b/libraries/base/Data/Semigroup.hs @@ -125,6 +125,21 @@ cycle1 :: Semigroup m => m -> m cycle1 xs = xs' where xs' = xs <> xs' -- | This lets you use a difference list of a 'Semigroup' as a 'Monoid'. +-- +-- >>> import Data.Semigroup +-- >>> let hello = diff "Hello, " +-- >>> appEndo hello "World!" +-- "Hello, World!" +-- >>> appEndo (hello <> mempty) "World!" +-- "Hello, World!" +-- >>> appEndo (mempty <> hello) "World!" +-- "Hello, World!" +-- >>> let world = diff "World" +-- >>> let excl = diff "!" +-- >>> print $ appEndo (hello <> (world <> excl)) mempty +-- "Hello, World!" +-- >>> print $ appEndo ((hello <> world) <> excl) mempty +-- "Hello, World!" diff :: Semigroup m => m -> Endo m diff = Endo . (<>) |