1 files changed, 19 insertions, 2 deletions

diff --git a/chain/src/default.rs b/chain/src/default.rs
index 7ee460c..da665bf 100644
--- a/chain/src/default.rs
+++ b/chain/src/default.rs
@@ -17,7 +17,10 @@ use graph::{
     labelled::DLGBuilder, Builder, DLGraph, Graph, LabelExtGraph, LabelGraph, ParentsGraph,
 };
 
-use std::collections::{HashMap as Map, HashSet, TryReserveError};
+use std::{
+    borrow::Borrow,
+    collections::{HashMap as Map, HashSet, TryReserveError},
+};
 
 /// The errors related to taking derivatives by chain rule.
 #[non_exhaustive]
@@ -194,6 +197,16 @@ impl Iterator for DerIter {
     }
 }
 
+// TODO: Add a hashmap mapping tuples of forest positions (top,
+// bottom) to vectors of tuples of unsigned integers.  Each tuple
+// represents a non-terminal and a rule.  The tuple means that we need
+// to close the expansion of the non-terminal by the rule position, if
+// we want to move from bottom to top.
+//
+// After we move up one layer, we are now in a new forest position, so
+// we just query again with the new bottom and top.  This means we do
+// not need to clear the map.
+
 /// A default implementation for the [`Chain`] trait.
 #[derive(Debug, Clone, Default)]
 pub struct DefaultChain {
@@ -739,7 +752,7 @@ impl Chain for DefaultChain {
                             let mut new_edges = Vec::new();
 
                             let virtual_accepting = generate_edges(
-                                self,
+                                self.borrow(),
                                 child_iter.clone(),
                                 atom_child_iter.clone(),
                                 first_segment_pavi,
@@ -753,6 +766,7 @@ impl Chain for DefaultChain {
 
                             if accepting {
                                 accepting_pavi.insert(virtual_pavi);
+                                // FIXME: set true_source here
                                 der_iter.singles.extend(new_edges.clone());
                             }
 
@@ -787,6 +801,8 @@ impl Chain for DefaultChain {
                                     if self.atom.is_empty_node(atom_child).unwrap() {
                                         // REVIEW: flat flat map,
                                         // hmm...
+
+                                        // FIXME: Set true_source as well.
                                         der_iter.singles.extend(child_iter.clone().flat_map(
                                             |child| {
                                                 self.graph.labels_of(child).unwrap().flat_map(
@@ -810,6 +826,7 @@ impl Chain for DefaultChain {
             }
         }
 
+        self.accepting_sources.clear();
         self.accepting_sources.extend(accepting_pavi);
 
         Ok(der_iter)