category-theory-presentation/categories/30_How/100_Functors/100_Non_Haskell_Hask_s_Functors.md

"Non Haskell" Hask's Functors

A simple basic example is the \(id_\Hask\) functor. It simply cannot be expressed as a couple (F,fmap) where

• F::* -> *
• fmap :: (a -> b) -> (F a) -> (F b)

Another example:

• F(T)=Int
• F(f)=\_->0