1 files changed, 12 insertions, 1 deletions
diff --git a/src/Ref.vala b/src/Ref.vala
index b1fd4e9..17ae2cf 100644
--- a/src/Ref.vala
+++ b/src/Ref.vala
@@ -1,5 +1,5 @@
 namespace Eva {
-  public class Ref : Object, Term {
+  public class Ref : Object, Term, Gee.Comparable<Ref> {
     public string node {get; construct;}
     public int len {get; construct;}
     public uint[] n {get; private set;}
@@ -22,6 +22,17 @@ namespace Eva {
       return "#Ref";
     }
     
+    public int compare_to(Ref o) {
+      for(int i = 0; i < len; ++i) {
+        if(n[i] < o.n[i])
+          return -1;
+        if(n[i] > o.n[i])
+          return 1;
+      }
+      
+      return 0;
+    }
+    
     protected bool do_match(Term o, Gee.Map<string, Term> vars, Gee.Map<string, string> aliases) {
       if(o is Var) {
         return o.do_match(this, vars, aliases);