# FSharpPlus Covariant Functor A [[Covariant Functor|Covariant Functor]] in FSharpPlus needs to have: - Map: `static member Map(x : 'Functor<'T>, f : 'T -> 'U)` (operator `map`) Implemented by: - [[FSharpPlus Const|Const]] - [[FSharpPlus Free|Free]] Sub types: - [[FSharpPlus Applicative Functor]] - [[FSharpPlus Bifunctor]]