How useful of monoid is

monoid1.hs

-- How Monoids are useful in Programming?
-- credit to https://www.youtube.com/watch?v=BovTQeDK7XI

module XMain where

import Data.Char
import Data.Monoid
import Data.Foldable

isValid :: Char -> Bool
isValid = getAll . foldMap (All .) predicates
    where
        predicates = [isAlpha, isLower]

isValid' :: Char -> Bool
isValid' = getAll . fold mPredicates
    where
        predicates = [isAlpha, isLower]
        mPredicates = map (All .) predicates

-- using sequence
isValid'' :: Char -> Bool
isValid'' = and . sequence [isAlpha, isLower]