map -package:containers -package:bytestring -package:dlist -package:base-prelude -package:monoidal-containers -package:blaze-html -package:insert-ordered-containers -package:integration -package:incipit-base -package:Cabal-syntax -package:charset -package:invertible package:pipes is:exact

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

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