diff options
Diffstat (limited to 'libraries/base/GHC/Base.hs')
| -rw-r--r-- | libraries/base/GHC/Base.hs | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/libraries/base/GHC/Base.hs b/libraries/base/GHC/Base.hs index 0ddd256426..c63ec1264f 100644 --- a/libraries/base/GHC/Base.hs +++ b/libraries/base/GHC/Base.hs @@ -211,6 +211,12 @@ infixr 6 <> -- -- [Associativity] @x '<>' (y '<>' z) = (x '<>' y) '<>' z@ -- +-- You can alternatively define `sconcat` instead of (`<>`), in which case the +-- laws are: +-- +-- [Unit]: @'sconcat' ('pure' x) = x@ +-- [Multiplication]: @'sconcat' ('join' xss) = 'sconcat' ('fmap' 'sconcat' xss)@ +-- -- @since 4.9.0.0 class Semigroup a where -- | An associative operation. @@ -218,6 +224,7 @@ class Semigroup a where -- >>> [1,2,3] <> [4,5,6] -- [1,2,3,4,5,6] (<>) :: a -> a -> a + a <> b = sconcat (a :| [ b ]) -- | Reduce a non-empty list with '<>' -- @@ -248,6 +255,8 @@ class Semigroup a where stimes :: Integral b => b -> a -> a stimes = stimesDefault + {-# MINIMAL (<>) | sconcat #-} + -- | The class of monoids (types with an associative binary operation that -- has an identity). Instances should satisfy the following: @@ -257,6 +266,13 @@ class Semigroup a where -- [Associativity] @x '<>' (y '<>' z) = (x '<>' y) '<>' z@ ('Semigroup' law) -- [Concatenation] @'mconcat' = 'foldr' ('<>') 'mempty'@ -- +-- You can alternatively define `mconcat` instead of `mempty`, in which case the +-- laws are: +-- +-- [Unit]: @'mconcat' ('pure' x) = x@ +-- [Multiplication]: @'mconcat' ('join' xss) = 'mconcat' ('fmap' 'mconcat' xss)@ +-- [Subclass]: @'mconcat' ('toList' xs) = 'sconcat' xs@ +-- -- The method names refer to the monoid of lists under concatenation, -- but there are many other instances. -- @@ -271,7 +287,9 @@ class Semigroup a => Monoid a where -- -- >>> "Hello world" <> mempty -- "Hello world" - mempty :: a + mempty :: a + mempty = mconcat [] + {-# INLINE mempty #-} -- | An associative operation -- @@ -297,6 +315,8 @@ class Semigroup a => Monoid a where {-# INLINE mconcat #-} -- INLINE in the hope of fusion with mconcat's argument (see !4890) + {-# MINIMAL mempty | mconcat #-} + -- | @since 4.9.0.0 instance Semigroup [a] where (<>) = (++) |