I have finally managed to upload a (dry version) of a note about representable functors in Haskell. You can find it here: http://covariant.me/notes/rep-functors.html

Representable functors are functors that are isomorphic to $Hom(A, -)$ or $Hom(-, A)$ for some object $A$. In the note I give examples of some simple representable functors and prove that `Maybe`

is not representable.