1 files changed, 27 insertions, 2 deletions
diff --git a/chain/src/lib.rs b/chain/src/lib.rs
index 9de1df7..bf3a8b4 100644
--- a/chain/src/lib.rs
+++ b/chain/src/lib.rs
@@ -240,6 +240,10 @@ pub trait Chain: LabelExtGraph<Edge> {
     /// language.
     fn unit(atom: Self::Atom) -> Result<Self, Self::Error>;
 
+    /// Produce the underlying atom, so that we can produce an initial
+    /// empty chain from the same atom again.
+    fn atom(&self) -> &Self::Atom;
+
     /// Return true if and only if the language contains the empty
     /// string.
     fn epsilon(&self) -> Result<bool, Self::Error>;
@@ -283,7 +287,8 @@ pub trait Chain: LabelExtGraph<Edge> {
     /// The argument `t` is the terminal we computet the derivative
     /// with.
     ///
-    /// The argument `pos` is the position within the input.
+    /// The argument `pos` is the zero-based position within the
+    /// input.
     ///
     /// The argument `no_item` determines whether we want the item
     /// derivation forest as well.
@@ -307,9 +312,29 @@ pub trait Chain: LabelExtGraph<Edge> {
         Ok(())
     }
 
+    // FIXME: I shall probably not use the trait of forests for this
+    // purpose, but I have not figured out yet wha the correct trait
+    // should be.
+    /// The type of output item that will be produced by this machine.
+    type Item: item::Forest<grammar::GrammarLabel>;
+
     /// Signal to the parser that the end of the input is reached, so
     /// that the parser knows to generate suitable forests.
-    fn end_of_input(&mut self) -> Result<(), Self::Error>;
+    ///
+    /// This is not needed when recognizing instead of parsing.
+    ///
+    /// We also pass in the current position `pos` so that we have a
+    /// little flexibility in the position of the end of input.  In
+    /// addition, this makes it easier to produce the suitable
+    /// forests.
+    ///
+    /// As a reminder, `pos` should be the position of the last
+    /// terminal, so if there are three terminals in total, the `pos`
+    /// should be `2` , instead of `3`.
+    ///
+    /// Similarly, we pass in the terminal at the position `pos` to
+    /// aid the production of the forest.
+    fn end_of_input(&mut self, pos: usize, ter: usize) -> Result<Self::Item, Self::Error>;
 }
 
 pub mod default;