fix build

Author: jkarneges

src/core/arena.rs

@@ -392,6 +392,11 @@ impl<T> Rc<T> {
         }
     }
 
+    #[inline]
+    pub fn ptr_eq(this: &Rc<T>, other: &Rc<T>) -> bool {
+        this.ptr.as_ptr() == other.ptr.as_ptr()
+    }
+
     #[inline(always)]
     pub fn get(&self) -> &T {
         &self.inner().value

src/core/list.rs

@@ -537,7 +537,7 @@ impl<T> RcNode<T> {
         if let Some(memory) = memory {
             match arena::Rc::new(data, memory) {
                 Ok(r) => Self::Arena(r),
-                Err(()) => unimplemented!(), // TODO: fall back to std
+                Err(arena::InsertError(data)) => Self::Std(Rc::new(data)),
             }
         } else {
             Self::Std(Rc::new(data))