From 9f501dcd09e7932fb650a1956a8343bea745a99e Mon Sep 17 00:00:00 2001
From: Jeremy Dormitzer <jeremy.dormitzer@gmail.com>
Date: Wed, 17 Jul 2019 22:44:11 -0400
Subject: [PATCH] Move rules ns to evaluator to avoid circular dependency

---
 src/sicp_logic/evaluator.clj | 59 ++++++++++++++++++++++++++++++++++--
 src/sicp_logic/rules.clj     | 56 ----------------------------------
 2 files changed, 56 insertions(+), 59 deletions(-)
 delete mode 100644 src/sicp_logic/rules.clj

diff --git a/src/sicp_logic/evaluator.clj b/src/sicp_logic/evaluator.clj
index 06a815a..5dd2d09 100644
--- a/src/sicp_logic/evaluator.clj
+++ b/src/sicp_logic/evaluator.clj
@@ -1,7 +1,8 @@
 (ns sicp-logic.evaluator
-  (:require [sicp-logic.binding :refer [instantiate]]
-            [sicp-logic.assertions :refer [find-assertions]]
-            [sicp-logic.rules :refer [apply-rules]]))
+  (:require [sicp-logic.assertions :refer [find-assertions]]
+            [sicp-logic.binding :refer [instantiate]]
+            [sicp-logic.db :refer [fetch-rules]]
+            [sicp-logic.match :refer [unify-match]]))
 
 (declare qeval)
 
@@ -47,6 +48,58 @@
        []))
    input-frames))
 
+;; Rule functions need to be in the same namespace as qeval to avoid
+;; a circular dependency, even though it would be more elegant to
+;; put them in a separate namespace.
+
+(defn rename-variables-in [rule]
+  "Gives all the variables in the rule globally unique names
+   to prevent name collisions during unification."
+  (let [bindings (atom {})
+        rename-var (fn [var]
+                     (let [var-name (second var)
+                           binding (get @bindings var-name)]
+                       (if binding
+                         binding
+                         (let [new-binding (gensym var-name)]
+                           (swap! bindings (fn [m] (assoc m var-name new-binding)))
+                           new-binding))))
+        rename-vars (fn rename-vars [exp]
+                      (cond
+                        (var? exp) (rename-var exp)
+                        (and (sequential? exp) (not (empty? exp)))
+                        (cons (rename-vars (first exp))
+                              (rename-vars (rest exp)))
+                        :else exp))]
+    (rename-vars rule)))
+
+
+(defn conclusion [rule]
+  "Selects the rule's conclusion")
+
+(defn rule-body [rule]
+  "Selects the rule's body")
+
+(defn apply-a-rule [rule query frame]
+  "Applies the `rule` to the `query` in the
+   `frame` by unifying the query with the rule to
+   produce a new frame then evaluating the body
+   of the rule in that new frame."
+  (let [clean-rule (rename-variables-in rule)
+        unify-result (unify-match query
+                                  (conclusion clean-rule)
+                                  frame)]
+    (if (= unify-result :failed)
+      []
+      (qeval (rule-body clean-rule)
+             [unify-result]))))
+
+(defn apply-rules [db query frame]
+  (mapcat
+   (fn [rule]
+     (apply-a-rule rule query frame))
+   (fetch-rules db query frame)))
+
 (defn simple-query [db q input-frames]
   "Processes a simple query, producing a sequence of frames with
    bindings for the variables in `q`."
diff --git a/src/sicp_logic/rules.clj b/src/sicp_logic/rules.clj
deleted file mode 100644
index 6779bcf..0000000
--- a/src/sicp_logic/rules.clj
+++ /dev/null
@@ -1,56 +0,0 @@
-(ns sicp-logic.rules
-  (:require [sicp-logic.binding :refer [var?]]
-            [sicp-logic.db :as db]
-            [sicp-logic.evaluator :refer [qeval]]
-            [sicp-logic.match :refer [unify-match]]))
-
-(defn rename-variables-in [rule]
-  "Gives all the variables in the rule globally unique names
-   to prevent name collisions during unification."
-  (let [bindings (atom {})
-        rename-var (fn [var]
-                     (let [var-name (second var)
-                           binding (get @bindings var-name)]
-                       (if binding
-                         binding
-                         (let [new-binding (gensym var-name)]
-                           (swap! bindings (fn [m] (assoc m var-name new-binding)))
-                           new-binding))))
-        rename-vars (fn rename-vars [exp]
-                      (cond
-                        (var? exp) (rename-var exp)
-                        (and (sequential? exp) (not (empty? exp)))
-                        (cons (rename-vars (first exp))
-                              (rename-vars (rest exp)))
-                        :else exp))]
-    (rename-vars rule)))
-
-
-(defn conclusion [rule]
-  "Selects the rule's conclusion")
-
-(defn rule-body [rule]
-  "Selects the rule's body")
-
-(defn apply-a-rule [rule query frame]
-  "Applies the `rule` to the `query` in the
-   `frame` by unifying the query with the rule to
-   produce a new frame then evaluating the body
-   of the rule in that new frame."
-  (let [clean-rule (rename-variables-in rule)
-        unify-result (unify-match query
-                                  (conclusion clean-rule)
-                                  frame)]
-    (if (= unify-result :failed)
-      []
-      (qeval (rule-body clean-rule)
-             [unify-result]))))
-
-(defn fetch-rules [db query frame]
-  (db/fetch-rules db query frame))
-
-(defn apply-rules [db query frame]
-  (mapcat
-   (fn [rule]
-     (apply-a-rule rule query frame))
-   (fetch-rules db query frame)))