Fix memory issues

src/types.h

@@ -110,6 +110,9 @@ GroundValue createBoolGroundValue(bool in);
 // Creates a GroundValue containing (in), with type LIST.
 GroundValue createListGroundValue(List in);
 
+// Creates a deep copy of a GroundValue
+GroundValue copyGroundValue(const GroundValue* gv);
+
 // If (gv) contains any data stored on the heap, frees it.
 void freeGroundValue(GroundValue* gv);
 
@@ -156,4 +159,4 @@ ListAccess getListAt(List* list, int idx);
 // Sets an item in list (list) at index (idx) to GroundValue (value).
 ListAccessStatus setListAt(List* list, int idx, GroundValue value);
 
-#endif
+#endif