Fixes flatten-bindings to keep unresolved lvars and also bindings to nil

Author: fogus

README.md

@@ -19,26 +19,26 @@ core.unify provides a la carte unification facilities that are not deeply tied i
 Releases and Dependency Information
 ========================================
 
-Latest stable release: 0.7.0
+Latest stable release: 0.7.1
 
 * [All Released Versions](https://search.maven.org/#search%7Cgav%7C1%7Cg%3A%22org.clojure%22%20AND%20a%3A%22core.unify%22)
 * [Development Snapshot Versions](https://oss.sonatype.org/index.html#nexus-search;gav~org.clojure~core.unify~~~)
 
 [CLI/`deps.edn`](https://clojure.org/reference/deps_and_cli) dependency information:
 ```clojure
-org.clojure/core.unify {:mvn/version "0.7.0"}
+org.clojure/core.unify {:mvn/version "0.7.1"}
 ```
 
 [Leiningen](https://github.com/technomancy/leiningen) dependency information:
 
-    [org.clojure/core.unify "0.7.0"]
+    [org.clojure/core.unify "0.7.1"]
 
 [Maven](https://maven.apache.org/) dependency information:
 
     <dependency>
       <groupId>org.clojure</groupId>
       <artifactId>core.unify</artifactId>
-      <version>0.7.0</version>
+      <version>0.7.1</version>
     </dependency>
 
 

deps.edn

@@ -6,7 +6,7 @@
            :1.9 {:override-deps {org.clojure/clojure {:mvn/version "1.9.0"}}}
            :1.10 {:override-deps {org.clojure/clojure {:mvn/version "1.10.3"}}}
            :1.11 {:override-deps {org.clojure/clojure {:mvn/version "1.11.4"}}}
-           :1.12 {:override-deps {org.clojure/clojure {:mvn/version "1.12.0"}}}
+           :1.12 {:override-deps {org.clojure/clojure {:mvn/version "1.12.4"}}}
            ;; suitable for Clojure 1.8 or later:
            :runner
            {:extra-deps {io.github.cognitect-labs/test-runner

src/main/clojure/clojure/core/unify.cljc

@@ -126,17 +126,17 @@
                                                                   binds)))))
 
 (defn flatten-bindings
-  "Flattens recursive bindings in the given map to the same ground (if possible)."
+  "Flattens recursive bindings in binds to the same ground, if possible.
+  If a variable cannot be resolved then it is left in place."
   ([binds] (flatten-bindings lvar? binds))
   ([variable? binds]
-     (into {}
-           (remove (comp nil? second)
-                   (map (fn [[k v]]
-                          [k (loop [v v]
-                               (if (variable? v)
-                                 (recur (binds v))
-                                 v))])
-                        binds)))))
+   (into {}
+         (map (fn [[k v]]
+                [k (loop [v v]
+                     (if-let [entry (and (variable? v) (find binds v))]
+                       (recur (val entry))
+                       v))])
+              binds))))
 
 (defn- try-subst
   [variable? x binds]

src/test/clojure/clojure/core/unify_test.cljc

@@ -9,7 +9,7 @@
 (ns ^{:doc "A unification library for Clojure."
       :author "Michael Fogus"}
   clojure.core.unify-test
-  (:require [clojure.core.unify :refer [unify]]
+  (:require [clojure.core.unify :refer [unify] :as u]
             [clojure.test :refer [deftest is testing]]))
 
 #?(:clj  (println "\nTesting with Clojure" (clojure-version))
@@ -63,7 +63,9 @@
   (is (= '{?y (2 3)}                       (#'clojure.core.unify/garner-unifiers '(_ & ?y) [1 2 3]))))
 
 (deftest test-flatten-bindings
-  (is (= '{?y a, ?x a}                     (#'clojure.core.unify/flatten-bindings '{?y a, ?x ?y}))))
+  (is (= '{?y a, ?x a}                     (u/flatten-bindings '{?y a, ?x ?y})))
+  (is (= '{?z a, ?x ?y}                    (u/flatten-bindings '{?x ?y, ?z a})))
+  (is (= {'?x nil}                         (u/flatten-bindings '{?x nil}))))
 
 
 (deftest test-unifier*