[Haskell-cafe] Why is (+++) not a functor?

[Felipe Almeida Lessa]

Hey! =)

ArrowChoice's (+++) documentation [1] says that "this is in general
not a functor" [1].  What does it mean for (+++) to be or not to be a
functor?

Cheers,

[1] http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/Control-Arrow.html#v:-43--43--43-

-- 
Felipe.