Functor

A type f is a Functor if it provides a function fmap which, given any types a and b lets you apply any function from (a -> b) to turn an f a into an f b, preserving the structure of f. Furthermore f needs to adhere to the following: Note, that the second law follows from the free theorem of the type fmap and the first law, so you need only check that the former condition holds. See these articles by School of Haskell or David Luposchainsky for an explanation.
A type f is a Functor if it provides a function fmap which, given any types a and b, lets you apply any function of type (a -> b) to turn an f a into an f b, preserving the structure of f.
The deriving code for the Functor, Foldable, and Traversable classes
Not on Stackage, so not searched. Functors
An adapter newtype, suitable for DerivingVia. Its Eq1, Ord1, Read1, and Show1 instances leverage Generic1-based defaults.
Not on Stackage, so not searched. Infix operators for mapping over compositions of functors. Lots of them.
Not on Stackage, so not searched. Tools for functor combinator-based program design
Not on Stackage, so not searched. General functor products for various Foldable instances
Not on Stackage, so not searched. This package has been subsumed by semigroupoids
Not on Stackage, so not searched. Data.Functor.Classes instances for core packages
Not on Stackage, so not searched. Functor combinators with tries & zippers
Not on Stackage, so not searched. Friendly helpers for your recursion schemes.
Not on Stackage, so not searched. FFunctor: functors on (the usual) Functors
Not on Stackage, so not searched. Monad-style combinators for functors.
Not on Stackage, so not searched. Collection of functor utilities, providing handy operators, like generalization of (.).
Not on Stackage, so not searched. Convert values from one type into another.
Not on Stackage, so not searched. Data.FunctorM (compatibility package)
Not on Stackage, so not searched. (.:) and friends, syntax for Functor and Applicative.