--- a/src/parallel_execution/compare.c	Mon Oct 10 20:19:26 2016 +0900
+++ b/src/parallel_execution/compare.c	Tue Oct 25 00:49:28 2016 +0900
@@ -1,11 +1,13 @@
 #include "context.h"
 
-void compare(struct Context* context, struct Traverse* traverse, int key1, int key2) {
+enum Relational compare(struct Node* node1, struct Node* node2) {
+    int key1 = node1->key;
+    int key2 = node2->key;
     if (key1 == key2) {
-        traverse->result = EQ;
+        return EQ;
     } else if (key1 < key2) {
-        traverse->result = GT;
+        return GT;
     } else {
-        traverse->result = LT;
+        return LT;
     }
 }