map -package:containers -package:insert-ordered-containers -package:ghc -package:invertible -package:case-insensitive -package:monoidal-containers -package:incipit-base -package:hedgehog -package:charset -package:integration -package:base-compat-batteries package:pipes is:exact

Apply a function to all values flowing downstream
map id = cat

map (g . f) = map f >-> map g