Folding Map
Folding map over list a la OCaml Core's folding map: https://ocaml.janestreet.com/ocaml-core/v0.12/doc/base/Base/List/index.html#val-folding_map
Folding map over list a la OCaml Core's folding map: https://ocaml.janestreet.com/ocaml-core/v0.12/doc/base/Base/List/index.html#val-folding_map