On Sun, Jul 2, 2017 at 9:51 PM, Marc Nieper-Wißkirchen <xxxxxx@nieper-wisskirchen.de> wrote:"Mappings form a new type as if created by define-record-type. It is an error to use record-type inspection or inheritance on the mapping type; i.e. the mapping type is sealed and opaque in the language of SRFI 99."This looks good to me. It prohibits overly ambiguous implementation (e.g. using alists), while allows an implementation to choose to use pre-existing native object as mapping.