From 918235659f7b0d80bfa305875ab7cc988cc51761 Mon Sep 17 00:00:00 2001
From: JSDurand <mmemmew@gmail.com>
Date: Fri, 16 Oct 2026 18:16:36 +0800
Subject: partial commit, before trying the new guide by claude

---
 chain/src/lib.rs | 72 +++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 56 insertions(+), 16 deletions(-)

(limited to 'chain/src/lib.rs')

diff --git a/chain/src/lib.rs b/chain/src/lib.rs
index 10143dd..24598a8 100644
--- a/chain/src/lib.rs
+++ b/chain/src/lib.rs
@@ -32,17 +32,21 @@ pub struct Edge {
     true_source: PaVi,
     /// Whether or not this edge is "accepting".
     accepting: bool,
+    /// The non-terminal that starts this edge.
+    frame_nt: usize,
 }
 
 impl Edge {
     /// Construct a new edge.
     pub fn new(label: usize, forest_source: PaVi, accepting: bool) -> Self {
         let true_source = forest_source;
+        let frame_nt = 0usize;
         Self {
             label,
             forest_source,
             accepting,
             true_source,
+            frame_nt,
         }
     }
 
@@ -61,6 +65,24 @@ impl Edge {
         self.forest_source
     }
 
+    /// Return the frame non-terminal of the edge.
+    pub fn frame_nt(&self) -> usize {
+        self.frame_nt
+    }
+
+    /// Set the frame non-terminal.
+    pub fn set_frame_nt(&mut self, nt: usize) {
+        self.frame_nt = nt;
+    }
+
+    /// Build a new edge with a given frame non-terminal.
+    pub fn with_frame_nt(self, nt: usize) -> Self {
+        Self {
+            frame_nt: nt,
+            ..self
+        }
+    }
+
     /// Set the associated forest edge of the edge of the edge.
     pub fn set_forest_source(&mut self, source: PaVi) {
         self.forest_source = source;
@@ -161,7 +183,7 @@ pub enum TwoLayers {
     /// the source of the associated forest edge of the second layer,
     /// and the third is a list of edges, which are the common first
     /// layers.
-    Two(usize, PaVi, bool, Vec<(Roi, usize)>),
+    Two(usize, PaVi, bool, usize, Vec<(Roi, usize)>),
 }
 
 /// The type of a collapsed iterator.
@@ -203,12 +225,22 @@ where
         if let Some(two_layer) = self.iter.next() {
             match two_layer {
                 TwoLayers::One(edge, to) => Some(Ok((edge, to))),
-                TwoLayers::Two(label, forest_source, accepting, edges) => {
-                    let new_index = match self.chain.extend(
-                        edges
-                            .into_iter()
-                            .filter_map(|(roi, target)| roi.real_part().map(|edge| (edge, target))),
-                    ) {
+                TwoLayers::Two(label, forest_source, accepting, frame_nt, edges) => {
+                    let imaginary: Vec<(Roi, usize)> = edges
+                        .iter()
+                        .filter(|(roi, _)| roi.imaginary_part().is_some())
+                        .map(|(roi, target)| (*roi, *target))
+                        .collect();
+
+                    let real: Vec<(Edge, usize)> = edges
+                        .into_iter()
+                        .filter_map(|(roi, target)| roi.real_part().map(|edge| (edge, target)))
+                        .collect();
+
+                    let new_index = match self
+                        .chain
+                        .extend(real.iter().map(|(edge, target)| (*edge, *target)))
+                    {
                         Ok(new) => new,
                         Err(error) => {
                             // Prevent further iterations.
@@ -218,8 +250,15 @@ where
                         }
                     };
 
+                    if let Err(err) = self.chain.update_epsilon(new_index, imaginary.into_iter()) {
+                        self.stop = true;
+                        return Some(Err(err));
+                    };
+
                     Some(Ok((
-                        Edge::new(label, forest_source, accepting).into(),
+                        Edge::new(label, forest_source, accepting)
+                            .with_frame_nt(frame_nt)
+                            .into(),
                         new_index,
                     )))
                 }
@@ -302,15 +341,16 @@ pub trait Chain: LabelExtGraph<Edge> {
 
         let edges = self.union(der_iter)?;
 
-        let new_index = self.extend(
-            edges
-                .iter()
-                .filter_map(|(roi, target)| roi.real_part().map(|edge| (edge, *target))),
-        )?;
+        let real: Vec<(Edge, usize)> = edges
+            .iter()
+            .filter_map(|(roi, target)| roi.real_part().map(|edge| (edge, *target)))
+            .collect();
 
-        if self.is_empty_node(new_index)? {
-            self.update_epsilon(new_index, edges.into_iter())?;
-        }
+        let new_index = self.extend(real.iter().map(|(edge, target)| (*edge, *target)))?;
+
+        // Imaginary edges can make the node accepting even when the
+        // node has real edges.
+        self.update_epsilon(new_index, edges.into_iter())?;
 
         self.update_history(new_index);
 
-- 
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