I'm soon about to do a new release of guile-log - logic programming in guile scheme. This release sports delimeted continution goals, an iso-prolog interface (it already sports a kanren interface) and much more.
Why guile-log's prolog? Well, for one thing, if you want to program future emacs in prolog, the base is now there. But it do sports a few interesting ideoms of it's own. But also it's possible to treat a prolog module as a scheme module and reuse already written prolog in e.g. a kanren program and of cause vice versa. It has been really tough to match an iso prolog at a reasonable level, but we will probably not have a stable solution until quite a few releases ahead of us. Also there is not much of a community so if you are interested in any of these aspects above please try contact me at the guile-user mailing list.
Anyway this is all for your fun, so have fun!! Cheers!