Haskell语言学习笔记（71）Semigroup

Semigroup

class Semigroup a where
        (<>) :: a -> a -> a
        sconcat :: NonEmpty a -> a
        stimes :: Integral b => b -> a -> a

class Semigroup a => Monoid a where
        mempty  :: a

        mappend :: a -> a -> a
        mappend = (<>)

        mconcat :: [a] -> a
        mconcat = foldr mappend mempty

半群（Semigroup）是个类型类，它是幺半群（Monoid）的基类。