clean up featurec

Fix horrible argument order. Update docstring for `partial-map`,
`partial-map` is no longer storable so cannot unify with logic
vars. Added docstring to `featurec`. Added `featurec` tests.

src/main/clojure/clojure/core/logic.clj

@@ -4006,24 +4006,16 @@
 
 (defn partial-map
   "Given map m, returns partial map that unifies with maps even if it
-   doesn't share all of the keys of that map.
-   Only the keys of the partial map will be unified:
-
-   (run* [q]
-     (fresh [pm x]
-       (== pm (partial-map {:a x}))
-       (== pm {:a 1 :b 2})
-       (== pm q)))
-   ;;=> ({:a 1})"
+   doesn't share all of the keys of that map."
   [m]
   (map->PMap m))
 
 (defn partial-map? [x]
   (instance? PMap x))
 
 (defn -featurec
-  ([fs x] (-featurec (partial-map fs) x nil))
-  ([fs x _id]
+  ([x fs] (-featurec x (partial-map fs) nil))
+  ([x fs _id]
      (reify
        clojure.lang.IFn
        (invoke [this a]
@@ -4034,15 +4026,15 @@
        (id [this] _id)
        IWithConstraintId
        (with-id [this _id]
-         (-featurec fs x _id))
+         (-featurec x fs _id))
        IConstraintOp
        (rator [_] `featurec)
-       (rands [_] [fs x])
+       (rands [_] [x])
        IReifiableConstraint
        (reifyc [_ v r a]
          (let [fs (into {} fs)
                r  (-reify* r (walk* a fs))]
-           `(featurec ~(walk* r fs) ~(walk* r x))))
+           `(featurec ~(walk* r x) ~(walk* r fs))))
        IRelevant
        (-relevant? [_ a] true)
        IRunnable
@@ -4051,8 +4043,13 @@
        IConstraintWatchedStores
        (watched-stores [this] #{::subst}))))
 
-(defn featurec [fs x]
-  (cgoal (-featurec fs x)))
+(defn featurec
+  "Ensure that a map contains at least the key-value pairs
+  in the map fs. fs must be partially instantiated - that is, 
+  it may contain values which are logic variables to support 
+  feature extraction."
+  [x fs]
+  (cgoal (-featurec x fs)))
 
 ;; =============================================================================
 ;; defc

src/test/clojure/clojure/core/logic/tests.clj

@@ -2635,6 +2635,27 @@
   (is (= (safefd)
          '([4 3 1 8 9 2 6 7 5]))))
 
+;; =============================================================================
+;; Feature Constraints
+
+(deftest test-featurec-1
+  (is (= (run* [q]
+           (featurec q {:foo 1}))
+         '((_0 :- (clojure.core.logic/featurec _0 {:foo 1})))))
+  (is (= (run* [q]
+           (featurec q {:foo 1})
+           (== q {:foo 1 :bar 2}))
+         '({:foo 1 :bar 2})))
+  (is (= (run* [q]
+           (featurec q {:foo 1})
+           (== q {:bar 2}))
+         ()))
+  (is (= (run* [q]
+           (fresh [x]
+             (featurec x {:foo q})
+             (== x {:foo 1})))
+         '(1))))
+
 ;; =============================================================================
 ;; Deep Constraints