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Can someone explain where Applicative instances arise in this code?
isAlphaNum :: Char -> Bool
isAlphaNum = (||) <$> isAlpha <*> isNum

s :: (r -> a -> b) -> (r -> a) -> r -> b
s f g x = f x (g x)

newtype Reader r a = Reader (r -> a)

f <*> x = c -> (f c) (x c)

isAlphaNum c = (isAlpha c) || (isNum c)

import Data.Char
import Control.Applicative

isAlphaNum = liftA2 (||) isAlpha isNumber

import Data.Char
import Control.Monad

isAlphaNum = liftM2 (||) isAlpha isNumber

import Data.Function

orFst = (||) `on` fst

-- orFst (True,3) (False, 7)
--> True