Well, Either is a monad. Evolution of this style to avoid divergent nesting depths (The Codoken: http://i.imgur.com/BtjZedW.jpg http://i.imgur.com/BtjZedW.jpg)

Well, Either is a monad. Evolution of this style to avoid divergent nesting depths (The Codoken: http://i.imgur.com/BtjZedW.jpg http://i.imgur.com/BtjZedW.jpg) is a monad, even in the "railway" style of F#.