REPL checkpoint

src/prolog/ast/logic/Predicate.kt

@@ -39,6 +39,11 @@ class Predicate : Resolvent {
      */
     fun add(clause: Clause) {
         require(clause.functor == functor) { "Clause functor does not match predicate functor" }
+
+        if (Debug.on) {
+            println("Adding clause $clause to predicate $functor")
+        }
+
         clauses.add(clause)
     }