You could eval the datalog macro to do it at runtime. I could also expose the underlying protocol that ! and ? use, which IS based on runtime symbols. That would be more like exposing a database engine API than a Datalog API though.
Jay On Fri, Aug 16, 2013 at 11:04 AM, Mikko Tiihonen <[email protected]> wrote: > Thank you for the clarification! > > Do I understand right that since the tables do not have any binding, there is > no way to parameterize them in runtime? The macro approach works if the table > is known in compile-time, but I am at loss to think of a way of providing the > table to the query in a variable that gets its value during runtime. > > Actually, since I'm doing just some preliminary exploration, this was a > valuable and timely piece of advice and I will return to the drawing board > and take this into consideration. > > Have a nice weekend! > > Best, > > Mikko T. > > Jay McCarthy kirjoitti 16.8.2013 kello 19:36: > >> The table position is not an expression position because tables are >> not values and do not have any binding. In particular, they are not >> symbols as you assume in your example. >> >> I could imagine trying to supporting something like your example, but >> it would be backwards incompatible and unlike any other Datalog system >> as far as I can tell. Do you have any opinions about this? >> >> You can do something similar with a simple macro: >> >> (define-syntax-rule (param-query table) >> (datalog family >> (? (table 'joseph2 X)))) >> >> (param-query parent) >> >> On Fri, Aug 16, 2013 at 5:08 AM, Mikko Tiihonen >> <[email protected]> wrote: >>> Hi! >>> >>> I've been trying to parameterize Datalog queries and have stumbled into a >>> problem with the tables in queries. As an example (from Datalog >>> documentation): >>> >>> #lang racket >>> (require datalog) >>> (define family (make-theory)) >>> (datalog family >>> (! (parent joseph2 joseph1)) >>> (! (parent joseph2 lucy)) >>> (! (parent joseph3 joseph2))) >>> >>> -now if I run the query as shown in the documentation >>> >>> (let ([x 'joseph2]) >>> (datalog family >>> (? (parent x X)))) >>> >>> the answer is as expected: >>> >>> '(#hasheq((X . joseph1)) #hasheq((X . lucy))) >>> >>> However, if I parameterize the table: >>> >>> (let ([x 'parent]) >>> (datalog family >>> (? (x 'joseph2 X)))) >>> >>> the query fails: >>> >>> '() >>> >>> Are there any workarounds for this? I am grateful for any suggestions... >>> >>> Best regards, >>> >>> Mikko Tiihonen >>> >>> >>> >>> >>> ____________________ >>> Racket Users list: >>> http://lists.racket-lang.org/users >> >> >> >> -- >> Jay McCarthy <[email protected]> >> Assistant Professor / Brigham Young University >> http://faculty.cs.byu.edu/~jay >> >> "The glory of God is Intelligence" - D&C 93 > -- Jay McCarthy <[email protected]> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93 ____________________ Racket Users list: http://lists.racket-lang.org/users
