Union type representing different EDN values. There are a few noteworthy cases where data structures differ slightly from their EDN counterparts. There are no equivalent "Maps" in Elm, so EdnMap is represented as (List (Edn, Edn)).

Similarly, a set is just a List Edn type because sets in Elm must be made from comparables.

Keywords are a tuple with the first item being an optional namespace.

Tags start with a tuple that contain the required namespace and tag name consecutively, before the EDN value that they annotate.