https://github.com/sonian/Greenmail/blob/master/src/clj/greenmail/db.clj#L98-L126 has an example, using clojure.core.logic/all to make a goal which is a conjunction of the clojure.core.logic/== goals
On 11/16/13, 5:04 PM, Mark wrote: > d'oh! Answering my own question: Just compose the unify functions a la > (unify (unify a v1 (:v1 r) v2 (:v2 r)) > > I have a feeling there is a library function/macro that would make this > less messy but I can't find it from the cheatsheet. > > On Saturday, November 16, 2013 10:31:50 AM UTC-8, Mark wrote: >> >> I stumbled across Timothy Baldridge's excellent video >> <http://www.youtube.com/watch?v=HHZ8iqswiCw>explaining how to incorporate >> data sources into core.logic. It reinvigorated my interest in using >> core.logic to query SQL RDBMS. I'm stumbling on a pretty simple thing, I >> think. I've got a table that has three columns, a single primary key >> column and two value columns. Using the pattern Tim outlines in his video, >> I've got a relation function that takes three parameters, one for each >> column and I'm trying to work through the case where the primary key is >> ground and the value columns are lvars. This translates to a query of the >> form SELECT v1, v2 FROM t WHERE pkey=?. Of course, this returns two values >> that must be unified. That's where I'm stuck. >> >> I know I want to return a substitution map, but I have two lvars to >> unify. How do I merge the two substitution maps? >> >> Sample code: >> (defn pkey-v1-v2-o [pkey v1 v2] >> (fn [a] >> (let [pkey (walk a pkey) >> v1 (walk a v1) >> v2(walk a v2)] >> (condp = [(not (lvar? pkey)) >> (not (lvar? v1)) >> (not (lvar? v2))] >> [true false false ] (to-stream >> (let [r (first (query ["SELECT v1, v2 FROM T >> WHERE pkey=?" pkey]))] >> (some-merge-fn (unify a v1 (:v1 r)) >> (unify a v2 (:v2 r))))))))) >> > -- And what is good, Phaedrus, And what is not good— Need we ask anyone to tell us these things?
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