Add not-pathc and get-c constraint functions

Author: hugoduncan

src/palletops/locos.clj

@@ -131,6 +131,13 @@
   [name & rules]
   `(def ~name (rules->logic-terms ~(vec (quote-rules rules)))))
 
+;; guarantee that a path of keys does not occur in map x
+(defc not-pathc [x path]
+  (= (get-in x path ::not-found) ::not-found))
+
+(defc get-c [x s]
+  (not= (get s x ::not-found) ::not-found))
+
 (defn matching-productions
   "Takes an expression, and applies rules to it, returning a sequence
    of valid productions."

test/palletops/locos_test.clj

@@ -69,3 +69,10 @@
     (is (= {:item :b} (apply-productions {:item :b} rules)))
     (is (= {:x 1} (apply-productions {} rules)))
     (is (= {:x 2 :a 1} (apply-productions {:a 1} rules)))))
+
+(deftest guard-test
+  (let [rules (rules [{:m ?a} {:x 1} (not-pathc ?a [:c :d])])]
+    (let [r (apply-rule-productions {:m {}} rules)]
+      (is (= {:m {} :x 1} r)))
+    (let [r (apply-rule-productions {:m {:c {:d 1}}} rules)]
+      (is (= {:m {:c {:d 1}}} r)))))