http://learnyouahaskell.com/higher-order-functions#function-applicationapp
http://lambda.jstolarek.com/2012/03/function-composition-and-dollar-operator-in-haskell/函数
其实这有关操做符的优先级(priority)和关联性(association) (这里用了"操做符"这个名称,可是其实Haskell里全是函数。。。)ci
微妙之差(至少在表面上看来), 不可不察.get
:)it