Let edge expansion terminate with the edge or the new child.

src/hidden/mutators.rs

@@ -399,7 +399,9 @@ impl<'a, T, S, A> EdgeExpander<'a, T, S, A> where T: Hash + Eq + Clone + 'a, S:
     /// added for `state`, initialized with the data produced by `g`. A parent
     /// edge pointing back to the vertex that this edge originates from will
     /// also be added, with initial data the value returned by `h`.
-    pub fn expand<G, H>(mut self, state: T, g: G, h: H) -> MutEdge<'a, T, S, A>
+    ///
+    /// Returns an edge handle for the newly expanded edge.
+    pub fn expand_to_edge<G, H>(mut self, state: T, g: G, h: H) -> MutEdge<'a, T, S, A>
         where G: FnOnce() -> S, H: FnOnce() -> A {
             let target_id = match self.graph.state_ids.get_or_insert(state) {
                 NamespaceInsertion::Present(target_id) => target_id,
@@ -413,4 +415,22 @@ impl<'a, T, S, A> EdgeExpander<'a, T, S, A> where T: Hash + Eq + Clone + 'a, S:
             self.arc_mut().target = Target::Expanded(target_id);
             MutEdge { graph: self.graph, id: self.id, }
         }
+
+    /// Expands this expander's edge, by connecting to the vertex associated
+    /// with the game state `state`.
+    ///
+    /// If `state` does not correspond to an extant vertex, a new vertex will be
+    /// added for `state`, initialized with the data produced by `g`. A parent
+    /// edge pointing back to the vertex that this edge originates from will
+    /// also be added, with initial data the value returned by `h`.
+    ///
+    /// Returns a node handle for the newly expanded edge's target.
+    pub fn expand_to_child<G, H>(self, state: T, g: G, h: H) -> MutNode<'a, T, S, A>
+        where G: FnOnce() -> S, H: FnOnce() -> A {
+            let edge = self.expand_to_edge(state, g, h);
+            match edge.to_target() {
+                Target::Expanded(n) => n,
+                Target::Unexpanded(_) => panic!("Edge expansion failed"),
+            }
+        }
 }