map -package:containers -package:insert-ordered-containers -package:monoidal-containers -package:base-prelude -package:dlist -is:exact -package:os-string -package:hedgehog -package:incipit-base -is:exact -package:Cabal-syntax -package:psqueues is:exact -package:case-insensitive package:pipes

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

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