Clojure Q&A - Recent questions and answers in core.logic

Answered: bug in core.logic with featurec searching for logic variables

Wed, 07 Dec 2022 22:59:19 +0000

featurec cannot have logic variables (ground or not) as keys

as a perquisite for logically dealing with maps with keys that are lvars, you have to be able to deal with sets that contain lvars (not just handling a set data structure, but understanding the logic of sets) and core.logic doesn't have code for that, so it both cannot handle logic on sets (https://clojure.atlassian.net/browse/LOGIC-56 was "fixed" by removing the nascent support core.logic had for sets because it wasn't logically correct) and cannot handle lvars as map keys.

Handling sets is a prereq for handling map keys because keys in a map are a set.

Answered: core.logic problem

Thu, 30 Sep 2021 05:26:48 +0000

I think you forgot to refer to == from core.logic, and are using clojure.core/== which explains the numbers error.

(require '[clojure.core.logic :as l]
         '[clojure.core.logic.pldb :as db])

(db/db-rel In-zone a b)

(def facts (db/db [In-zone 'A 'B])) 

(println
   (db/with-db facts
    (l/run* [q]
      (l/fresh [x y]
        (In-zone x y)
        (l/== q [x y])))))

;;([A B])

Answered: clojure.core.logic/project returning LVar instead of bound value

Wed, 12 May 2021 22:02:46 +0000

the fact that you are getting an lvar out of project means there isn't a "current value of the LVar vhead"

Project is non-relational, what this largely means is it is very order dependent,

for example:

user=> (doall (l/run 1 [q] (l/fresh []  (l/== q 1) (l/project [q] (do (println q) l/succeed)))))
1
(1)
user=> (doall (l/run 1 [q] (l/fresh [] (l/project [q] (do (println q) l/succeed)) (l/== q 1))))
<lvar:q__3358>
(1)
user=>

So when you get an lvar instead of the value you expect, it is because the goals that you expect to assign a value to the lvar have not been executed yet.

I don't know what your level of experience is with core.logic/prolog/minikanren, but if are starting out/learning, I recommend forgetting that project exists. It can be a useful hack(for debugging, performance, or for writing interfaces between core.logic and other systems), but if your goal is to write logic programs, it will get in your way.

Answered: Can core.logic reason about sets?

Fri, 15 Jan 2021 14:28:22 +0000

Curious if you could wrangle something (at least membership) via featurec

I think the set-to-list is idiomatic though.

Answered: Memoization in core.logic

Sun, 29 Nov 2020 12:23:05 +0000

Never tried it, but I think it's called "tabling" in clojure.core.logic. Does tabled help? https://clojure.github.io/core.logic/#clojure.core.logic/tabled

Answered: If a map is a coll, why can't conso take its first element?

Sun, 24 Nov 2019 21:11:51 +0000

Conso only works for ordered collections, which is why it does not work for sets and maps. Without order there is no meaningful notion of first and rest. I would agree that the documentation for conso could be clarified by prepending "ordered" to collection.

Answered: lein deps and lein classpath fail for current core.logic, where to report?

Wed, 06 Nov 2019 01:34:34 +0000

The project.clj file for this project is not used, which is likely why it's out of date and not working This is a Maven project, and the pom.xml is the canonical project file here.

I'm happy to fix the project.clj, but it's really not the way to run stuff for this project.

Answered: Add non-interleaving version of conde