thank you! the scryer community deserves much of the credit too. everyone is welcome and encouraged to join us at https://github.com/mthom/scryer-prolog! some exciting plans in the pipe
Several innovations are documented in the README. Both the Prolog implementation and the type checker are written in / hosted by Scryer (Prolog implementation is done, the type checker is in progress). Scryer has many powerful constructs for monotonic reasoning which should help to take Shen's type checker in particular to new heights of power!