map -package:basement -package:bytestring -package:base-compat package:insert-ordered-containers

Order preserving mapping of keys.
HashMap which tries its best to remember insertion order of elements.
This is a slight lie, as roundtrip doesn't preserve ordering.
More efficient than foldMap, when folding in insertion order is not important.
More efficient than foldMapWithKey, when folding in insertion order is not important.