print ops properly.

src/prolog/tabled_rc.rs

@@ -0,0 +1,36 @@
+use std::cell::RefCell;
+use std::collections::HashSet;
+use std::hash::Hash;
+use std::ops::Deref;
+use std::rc::Rc;
+
+pub type TabledData<T> = HashSet<Rc<T>>;
+    
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct TabledRc<T: Hash + Eq> {
+    atom: Rc<T>,
+    table: Rc<RefCell<TabledData<T>>>
+}
+
+impl<T: Hash + Eq> TabledRc<T> {
+    pub fn new(atom: T, table: Rc<RefCell<TabledData<T>>>) -> Self {
+        TabledRc { atom: Rc::new(atom), table }
+    }
+}
+
+impl<T: Hash + Eq> Drop for TabledRc<T> {
+    fn drop(&mut self) {
+        if Rc::strong_count(&self.atom) == 2 {
+            let table = *self.table.borrow_mut();
+            table.remove(&self.atom);
+        }
+    }
+}
+
+impl<T: Hash + Eq> Deref for TabledRc<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &*self.atom
+    }
+}