diff --git a/lib/bforest/src/lib.rs b/lib/bforest/src/lib.rs
index 1bddcd8a73..2a1c5f8436 100644
--- a/lib/bforest/src/lib.rs
+++ b/lib/bforest/src/lib.rs
@@ -114,9 +114,6 @@ trait Forest {
     /// An array of values for the leaf nodes.
     type LeafValues: Copy + BorrowMut<[Self::Value]>;
 
-    /// Type used for key comparisons.
-    type Comparator: Comparator<Self::Key>;
-
     /// Splat a single key into a whole array.
     fn splat_key(key: Self::Key) -> Self::LeafKeys;
 
diff --git a/lib/bforest/src/map.rs b/lib/bforest/src/map.rs
index 270d186230..497ca2c112 100644
--- a/lib/bforest/src/map.rs
+++ b/lib/bforest/src/map.rs
@@ -9,19 +9,17 @@ use std::marker::PhantomData;
 use std::string::String;
 
 /// Tag type defining forest types for a map.
-struct MapTypes<K, V, C>(PhantomData<(K, V, C)>);
+struct MapTypes<K, V>(PhantomData<(K, V)>);
 
-impl<K, V, C> Forest for MapTypes<K, V, C>
+impl<K, V> Forest for MapTypes<K, V>
 where
     K: Copy,
     V: Copy,
-    C: Comparator<K>,
 {
     type Key = K;
     type Value = V;
     type LeafKeys = [K; INNER_SIZE - 1];
     type LeafValues = [V; INNER_SIZE - 1];
-    type Comparator = C;
 
     fn splat_key(key: Self::Key) -> Self::LeafKeys {
         [key; INNER_SIZE - 1]
@@ -33,20 +31,18 @@ where
 }
 
 /// Memory pool for a forest of `Map` instances.
-pub struct MapForest<K, V, C>
+pub struct MapForest<K, V>
 where
     K: Copy,
     V: Copy,
-    C: Comparator<K>,
 {
-    nodes: NodePool<MapTypes<K, V, C>>,
+    nodes: NodePool<MapTypes<K, V>>,
 }
 
-impl<K, V, C> MapForest<K, V, C>
+impl<K, V> MapForest<K, V>
 where
     K: Copy,
     V: Copy,
-    C: Comparator<K>,
 {
     /// Create a new empty forest.
     pub fn new() -> Self {
@@ -63,7 +59,7 @@ where
     }
 }
 
-/// B-tree mapping from `K` to `V` using `C` for comparing keys.
+/// B-tree mapping from `K` to `V`.
 ///
 /// This is not a general-purpose replacement for `BTreeMap`. See the [module
 /// documentation](index.html) for more information about design tradeoffs.
@@ -72,21 +68,19 @@ where
 /// they belong to. *Cloning a map does not allocate new memory for the clone*. It creates an alias
 /// of the same memory.
 #[derive(Clone)]
-pub struct Map<K, V, C>
+pub struct Map<K, V>
 where
     K: Copy,
     V: Copy,
-    C: Comparator<K>,
 {
     root: PackedOption<Node>,
-    unused: PhantomData<(K, V, C)>,
+    unused: PhantomData<(K, V)>,
 }
 
-impl<K, V, C> Map<K, V, C>
+impl<K, V> Map<K, V>
 where
     K: Copy,
     V: Copy,
-    C: Comparator<K>,
 {
     /// Make an empty map.
     pub fn new() -> Self {
@@ -102,7 +96,7 @@ where
     }
 
     /// Get the value stored for `key`.
-    pub fn get(&self, key: K, forest: &MapForest<K, V, C>, comp: &C) -> Option<V> {
+    pub fn get<C: Comparator<K>>(&self, key: K, forest: &MapForest<K, V>, comp: &C) -> Option<V> {
         self.root
             .expand()
             .and_then(|root| Path::default().find(key, root, &forest.nodes, comp))
@@ -115,7 +109,12 @@ where
     /// Otherwise, return the last key-value pair with a key that is less than or equal to `key`.
     ///
     /// If no stored keys are less than or equal to `key`, return `None`.
-    pub fn get_or_less(&self, key: K, forest: &MapForest<K, V, C>, comp: &C) -> Option<(K, V)> {
+    pub fn get_or_less<C: Comparator<K>>(
+        &self,
+        key: K,
+        forest: &MapForest<K, V>,
+        comp: &C,
+    ) -> Option<(K, V)> {
         self.root.expand().and_then(|root| {
             let mut path = Path::default();
             match path.find(key, root, &forest.nodes, comp) {
@@ -126,18 +125,23 @@ where
     }
 
     /// Insert `key, value` into the map and return the old value stored for `key`, if any.
-    pub fn insert(
+    pub fn insert<C: Comparator<K>>(
         &mut self,
         key: K,
         value: V,
-        forest: &mut MapForest<K, V, C>,
+        forest: &mut MapForest<K, V>,
         comp: &C,
     ) -> Option<V> {
         self.cursor(forest, comp).insert(key, value)
     }
 
     /// Remove `key` from the map and return the removed value for `key`, if any.
-    pub fn remove(&mut self, key: K, forest: &mut MapForest<K, V, C>, comp: &C) -> Option<V> {
+    pub fn remove<C: Comparator<K>>(
+        &mut self,
+        key: K,
+        forest: &mut MapForest<K, V>,
+        comp: &C,
+    ) -> Option<V> {
         let mut c = self.cursor(forest, comp);
         if c.goto(key).is_some() {
             c.remove()
@@ -147,7 +151,7 @@ where
     }
 
     /// Remove all entries.
-    pub fn clear(&mut self, forest: &mut MapForest<K, V, C>) {
+    pub fn clear(&mut self, forest: &mut MapForest<K, V>) {
         if let Some(root) = self.root.take() {
             forest.nodes.free_tree(root);
         }
@@ -158,7 +162,7 @@ where
     /// Remove all key-value pairs where the predicate returns false.
     ///
     /// The predicate is allowed to update the values stored in the map.
-    pub fn retain<F>(&mut self, forest: &mut MapForest<K, V, C>, mut predicate: F)
+    pub fn retain<F>(&mut self, forest: &mut MapForest<K, V>, mut predicate: F)
     where
         F: FnMut(K, &mut V) -> bool,
     {
@@ -181,16 +185,16 @@ where
 
     /// Create a cursor for navigating this map. The cursor is initially positioned off the end of
     /// the map.
-    pub fn cursor<'a>(
+    pub fn cursor<'a, C: Comparator<K>>(
         &'a mut self,
-        forest: &'a mut MapForest<K, V, C>,
+        forest: &'a mut MapForest<K, V>,
         comp: &'a C,
     ) -> MapCursor<'a, K, V, C> {
         MapCursor::new(self, forest, comp)
     }
 
     /// Create an iterator traversing this map. The iterator type is `(K, V)`.
-    pub fn iter<'a>(&'a self, forest: &'a MapForest<K, V, C>) -> MapIter<'a, K, V, C> {
+    pub fn iter<'a>(&'a self, forest: &'a MapForest<K, V>) -> MapIter<'a, K, V> {
         MapIter {
             root: self.root,
             pool: &forest.nodes,
@@ -199,11 +203,10 @@ where
     }
 }
 
-impl<K, V, C> Default for Map<K, V, C>
+impl<K, V> Default for Map<K, V>
 where
     K: Copy,
     V: Copy,
-    C: Comparator<K>,
 {
     fn default() -> Self {
         Self::new()
@@ -211,16 +214,15 @@ where
 }
 
 #[cfg(test)]
-impl<K, V, C> Map<K, V, C>
+impl<K, V> Map<K, V>
 where
     K: Copy + fmt::Display,
     V: Copy,
-    C: Comparator<K>,
 {
     /// Verify consistency.
-    fn verify(&self, forest: &MapForest<K, V, C>, comp: &C)
+    fn verify<C: Comparator<K>>(&self, forest: &MapForest<K, V>, comp: &C)
     where
-        NodeData<MapTypes<K, V, C>>: fmt::Display,
+        NodeData<MapTypes<K, V>>: fmt::Display,
     {
         if let Some(root) = self.root.expand() {
             forest.nodes.verify_tree(root, comp);
@@ -228,7 +230,7 @@ where
     }
 
     /// Get a text version of the path to `key`.
-    fn tpath(&self, key: K, forest: &MapForest<K, V, C>, comp: &C) -> String {
+    fn tpath<C: Comparator<K>>(&self, key: K, forest: &MapForest<K, V>, comp: &C) -> String {
         use std::string::ToString;
         match self.root.expand() {
             None => "map(empty)".to_string(),
@@ -252,9 +254,9 @@ where
     C: 'a + Comparator<K>,
 {
     root: &'a mut PackedOption<Node>,
-    pool: &'a mut NodePool<MapTypes<K, V, C>>,
+    pool: &'a mut NodePool<MapTypes<K, V>>,
     comp: &'a C,
-    path: Path<MapTypes<K, V, C>>,
+    path: Path<MapTypes<K, V>>,
 }
 
 impl<'a, K, V, C> MapCursor<'a, K, V, C>
@@ -265,8 +267,8 @@ where
 {
     /// Create a cursor with a default (off-the-end) location.
     fn new(
-        container: &'a mut Map<K, V, C>,
-        forest: &'a mut MapForest<K, V, C>,
+        container: &'a mut Map<K, V>,
+        forest: &'a mut MapForest<K, V>,
         comp: &'a C,
     ) -> MapCursor<'a, K, V, C> {
         MapCursor {
@@ -379,22 +381,20 @@ where
 }
 
 /// An iterator visiting the key-value pairs of a `Map`.
-pub struct MapIter<'a, K, V, C>
+pub struct MapIter<'a, K, V>
 where
     K: 'a + Copy,
     V: 'a + Copy,
-    C: 'a + Comparator<K>,
 {
     root: PackedOption<Node>,
-    pool: &'a NodePool<MapTypes<K, V, C>>,
-    path: Path<MapTypes<K, V, C>>,
+    pool: &'a NodePool<MapTypes<K, V>>,
+    path: Path<MapTypes<K, V>>,
 }
 
-impl<'a, K, V, C> Iterator for MapIter<'a, K, V, C>
+impl<'a, K, V> Iterator for MapIter<'a, K, V>
 where
     K: 'a + Copy,
     V: 'a + Copy,
-    C: 'a + Comparator<K>,
 {
     type Item = (K, V);
 
@@ -438,16 +438,16 @@ mod test {
     #[test]
     fn node_size() {
         // check that nodes are cache line sized when keys and values are 32 bits.
-        type F = MapTypes<u32, u32, ()>;
+        type F = MapTypes<u32, u32>;
         assert_eq!(mem::size_of::<NodeData<F>>(), 64);
     }
 
     #[test]
     fn empty() {
-        let mut f = MapForest::<u32, f32, ()>::new();
+        let mut f = MapForest::<u32, f32>::new();
         f.clear();
 
-        let mut m = Map::<u32, f32, ()>::new();
+        let mut m = Map::<u32, f32>::new();
         assert!(m.is_empty());
         m.clear(&mut f);
 
@@ -470,8 +470,8 @@ mod test {
 
     #[test]
     fn inserting() {
-        let f = &mut MapForest::<u32, f32, ()>::new();
-        let mut m = Map::<u32, f32, ()>::new();
+        let f = &mut MapForest::<u32, f32>::new();
+        let mut m = Map::<u32, f32>::new();
 
         // The first seven values stay in a single leaf node.
         assert_eq!(m.insert(50, 5.0, f, &()), None);
@@ -577,9 +577,9 @@ mod test {
     #[test]
     fn split_level0_leaf() {
         // Various ways of splitting a full leaf node at level 0.
-        let f = &mut MapForest::<u32, f32, ()>::new();
+        let f = &mut MapForest::<u32, f32>::new();
 
-        fn full_leaf(f: &mut MapForest<u32, f32, ()>) -> Map<u32, f32, ()> {
+        fn full_leaf(f: &mut MapForest<u32, f32>) -> Map<u32, f32> {
             let mut m = Map::new();
             for n in 1..8 {
                 m.insert(n * 10, n as f32 * 1.1, f, &());
@@ -628,7 +628,7 @@ mod test {
     #[test]
     fn split_level1_leaf() {
         // Various ways of splitting a full leaf node at level 1.
-        let f = &mut MapForest::<u32, f32, ()>::new();
+        let f = &mut MapForest::<u32, f32>::new();
 
         // Return a map whose root node is a full inner node, and the leaf nodes are all full
         // containing:
@@ -637,7 +637,7 @@ mod test {
         // 210, 220, ..., 270
         // ...
         // 810, 820, ..., 870
-        fn full(f: &mut MapForest<u32, f32, ()>) -> Map<u32, f32, ()> {
+        fn full(f: &mut MapForest<u32, f32>) -> Map<u32, f32> {
             let mut m = Map::new();
 
             // Start by inserting elements in order.
@@ -756,7 +756,7 @@ mod test {
 
     // Make a tree with two barely healthy leaf nodes:
     // [ 10 20 30 40 ] [ 50 60 70 80 ]
-    fn two_leaf(f: &mut MapForest<u32, f32, ()>) -> Map<u32, f32, ()> {
+    fn two_leaf(f: &mut MapForest<u32, f32>) -> Map<u32, f32> {
         f.clear();
         let mut m = Map::new();
         for n in 1..9 {
@@ -767,7 +767,7 @@ mod test {
 
     #[test]
     fn remove_level1() {
-        let f = &mut MapForest::<u32, f32, ()>::new();
+        let f = &mut MapForest::<u32, f32>::new();
         let mut m = two_leaf(f);
 
         // Verify geometry.
@@ -830,7 +830,7 @@ mod test {
 
     #[test]
     fn remove_level1_rightmost() {
-        let f = &mut MapForest::<u32, f32, ()>::new();
+        let f = &mut MapForest::<u32, f32>::new();
         let mut m = two_leaf(f);
 
         // [ 10 20 30 40 ] [ 50 60 70 80 ]
@@ -852,7 +852,7 @@ mod test {
 
     // Make a 3-level tree with barely healthy nodes.
     // 1 root, 8 inner nodes, 7*4+5=33 leaf nodes, 4 entries each.
-    fn level3_sparse(f: &mut MapForest<u32, f32, ()>) -> Map<u32, f32, ()> {
+    fn level3_sparse(f: &mut MapForest<u32, f32>) -> Map<u32, f32> {
         f.clear();
         let mut m = Map::new();
         for n in 1..133 {
@@ -863,7 +863,7 @@ mod test {
 
     #[test]
     fn level3_removes() {
-        let f = &mut MapForest::<u32, f32, ()>::new();
+        let f = &mut MapForest::<u32, f32>::new();
         let mut m = level3_sparse(f);
         m.verify(f, &());
 
@@ -894,8 +894,8 @@ mod test {
 
     #[test]
     fn insert_many() {
-        let f = &mut MapForest::<u32, f32, ()>::new();
-        let mut m = Map::<u32, f32, ()>::new();
+        let f = &mut MapForest::<u32, f32>::new();
+        let mut m = Map::<u32, f32>::new();
 
         let mm = 4096;
         let mut x = 0;
diff --git a/lib/bforest/src/node.rs b/lib/bforest/src/node.rs
index b529816afb..de5337053d 100644
--- a/lib/bforest/src/node.rs
+++ b/lib/bforest/src/node.rs
@@ -595,7 +595,6 @@ mod test {
         type Value = SetValue;
         type LeafKeys = [char; 15];
         type LeafValues = [SetValue; 15];
-        type Comparator = ();
 
         fn splat_key(key: Self::Key) -> Self::LeafKeys {
             [key; 15]
diff --git a/lib/bforest/src/path.rs b/lib/bforest/src/path.rs
index c0e4a089af..153c487547 100644
--- a/lib/bforest/src/path.rs
+++ b/lib/bforest/src/path.rs
@@ -49,7 +49,7 @@ impl<F: Forest> Path<F> {
         key: F::Key,
         root: Node,
         pool: &NodePool<F>,
-        comp: &F::Comparator,
+        comp: &Comparator<F::Key>,
     ) -> Option<F::Value> {
         let mut node = root;
         for level in 0.. {
@@ -723,7 +723,6 @@ mod test {
         type Value = char;
         type LeafKeys = [i32; 7];
         type LeafValues = [char; 7];
-        type Comparator = TC;
 
         fn splat_key(key: Self::Key) -> Self::LeafKeys {
             [key; 7]
diff --git a/lib/bforest/src/pool.rs b/lib/bforest/src/pool.rs
index e6b08e4f1c..ceab96d38c 100644
--- a/lib/bforest/src/pool.rs
+++ b/lib/bforest/src/pool.rs
@@ -1,5 +1,7 @@
 //! B+-tree node pool.
 
+#[cfg(test)]
+use super::Comparator;
 use super::{Forest, Node, NodeData};
 use entity::PrimaryMap;
 #[cfg(test)]
@@ -76,12 +78,11 @@ impl<F: Forest> NodePool<F> {
 #[cfg(test)]
 impl<F: Forest> NodePool<F> {
     /// Verify the consistency of the tree rooted at `node`.
-    pub fn verify_tree(&self, node: Node, comp: &F::Comparator)
+    pub fn verify_tree<C: Comparator<F::Key>>(&self, node: Node, comp: &C)
     where
         NodeData<F>: fmt::Display,
         F::Key: fmt::Display,
     {
-        use super::Comparator;
         use entity::SparseSet;
         use std::borrow::Borrow;
         use std::cmp::Ordering;
diff --git a/lib/bforest/src/set.rs b/lib/bforest/src/set.rs
index 8371fd3bc6..911907ee61 100644
--- a/lib/bforest/src/set.rs
+++ b/lib/bforest/src/set.rs
@@ -9,18 +9,16 @@ use std::marker::PhantomData;
 use std::string::String;
 
 /// Tag type defining forest types for a set.
-struct SetTypes<K, C>(PhantomData<(K, C)>);
+struct SetTypes<K>(PhantomData<K>);
 
-impl<K, C> Forest for SetTypes<K, C>
+impl<K> Forest for SetTypes<K>
 where
     K: Copy,
-    C: Comparator<K>,
 {
     type Key = K;
     type Value = SetValue;
     type LeafKeys = [K; 2 * INNER_SIZE - 1];
     type LeafValues = [SetValue; 2 * INNER_SIZE - 1];
-    type Comparator = C;
 
     fn splat_key(key: Self::Key) -> Self::LeafKeys {
         [key; 2 * INNER_SIZE - 1]
@@ -32,18 +30,16 @@ where
 }
 
 /// Memory pool for a forest of `Set` instances.
-pub struct SetForest<K, C>
+pub struct SetForest<K>
 where
     K: Copy,
-    C: Comparator<K>,
 {
-    nodes: NodePool<SetTypes<K, C>>,
+    nodes: NodePool<SetTypes<K>>,
 }
 
-impl<K, C> SetForest<K, C>
+impl<K> SetForest<K>
 where
     K: Copy,
-    C: Comparator<K>,
 {
     /// Create a new empty forest.
     pub fn new() -> Self {
@@ -69,19 +65,17 @@ where
 /// they belong to. *Cloning a set does not allocate new memory for the clone*. It creates an alias
 /// of the same memory.
 #[derive(Clone)]
-pub struct Set<K, C>
+pub struct Set<K>
 where
     K: Copy,
-    C: Comparator<K>,
 {
     root: PackedOption<Node>,
-    unused: PhantomData<(K, C)>,
+    unused: PhantomData<K>,
 }
 
-impl<K, C> Set<K, C>
+impl<K> Set<K>
 where
     K: Copy,
-    C: Comparator<K>,
 {
     /// Make an empty set.
     pub fn new() -> Self {
@@ -97,7 +91,7 @@ where
     }
 
     /// Does the set contain `key`?.
-    pub fn contains(&self, key: K, forest: &SetForest<K, C>, comp: &C) -> bool {
+    pub fn contains<C: Comparator<K>>(&self, key: K, forest: &SetForest<K>, comp: &C) -> bool {
         self.root
             .expand()
             .and_then(|root| Path::default().find(key, root, &forest.nodes, comp))
@@ -109,14 +103,24 @@ where
     /// If the set did not contain `key`, insert it and return true.
     ///
     /// If `key` is already present, don't change the set and return false.
-    pub fn insert(&mut self, key: K, forest: &mut SetForest<K, C>, comp: &C) -> bool {
+    pub fn insert<C: Comparator<K>>(
+        &mut self,
+        key: K,
+        forest: &mut SetForest<K>,
+        comp: &C,
+    ) -> bool {
         self.cursor(forest, comp).insert(key)
     }
 
     /// Remove `key` from the set and return true.
     ///
     /// If `key` was not present in the set, return false.
-    pub fn remove(&mut self, key: K, forest: &mut SetForest<K, C>, comp: &C) -> bool {
+    pub fn remove<C: Comparator<K>>(
+        &mut self,
+        key: K,
+        forest: &mut SetForest<K>,
+        comp: &C,
+    ) -> bool {
         let mut c = self.cursor(forest, comp);
         if c.goto(key) {
             c.remove();
@@ -127,7 +131,7 @@ where
     }
 
     /// Remove all entries.
-    pub fn clear(&mut self, forest: &mut SetForest<K, C>) {
+    pub fn clear(&mut self, forest: &mut SetForest<K>) {
         if let Some(root) = self.root.take() {
             forest.nodes.free_tree(root);
         }
@@ -136,7 +140,7 @@ where
     /// Retains only the elements specified by the predicate.
     ///
     /// Remove all elements where the predicate returns false.
-    pub fn retain<F>(&mut self, forest: &mut SetForest<K, C>, mut predicate: F)
+    pub fn retain<F>(&mut self, forest: &mut SetForest<K>, mut predicate: F)
     where
         F: FnMut(K) -> bool,
     {
@@ -155,16 +159,16 @@ where
 
     /// Create a cursor for navigating this set. The cursor is initially positioned off the end of
     /// the set.
-    pub fn cursor<'a>(
+    pub fn cursor<'a, C: Comparator<K>>(
         &'a mut self,
-        forest: &'a mut SetForest<K, C>,
+        forest: &'a mut SetForest<K>,
         comp: &'a C,
     ) -> SetCursor<'a, K, C> {
         SetCursor::new(self, forest, comp)
     }
 
     /// Create an iterator traversing this set. The iterator type is `K`.
-    pub fn iter<'a>(&'a self, forest: &'a SetForest<K, C>) -> SetIter<'a, K, C> {
+    pub fn iter<'a>(&'a self, forest: &'a SetForest<K>) -> SetIter<'a, K> {
         SetIter {
             root: self.root,
             pool: &forest.nodes,
@@ -173,10 +177,9 @@ where
     }
 }
 
-impl<K, C> Default for Set<K, C>
+impl<K> Default for Set<K>
 where
     K: Copy,
-    C: Comparator<K>,
 {
     fn default() -> Self {
         Self::new()
@@ -193,9 +196,9 @@ where
     C: 'a + Comparator<K>,
 {
     root: &'a mut PackedOption<Node>,
-    pool: &'a mut NodePool<SetTypes<K, C>>,
+    pool: &'a mut NodePool<SetTypes<K>>,
     comp: &'a C,
-    path: Path<SetTypes<K, C>>,
+    path: Path<SetTypes<K>>,
 }
 
 impl<'a, K, C> SetCursor<'a, K, C>
@@ -205,8 +208,8 @@ where
 {
     /// Create a cursor with a default (invalid) location.
     fn new(
-        container: &'a mut Set<K, C>,
-        forest: &'a mut SetForest<K, C>,
+        container: &'a mut Set<K>,
+        forest: &'a mut SetForest<K>,
         comp: &'a C,
     ) -> SetCursor<'a, K, C> {
         SetCursor {
@@ -327,20 +330,18 @@ where
 }
 
 /// An iterator visiting the elements of a `Set`.
-pub struct SetIter<'a, K, C>
+pub struct SetIter<'a, K>
 where
     K: 'a + Copy,
-    C: 'a + Comparator<K>,
 {
     root: PackedOption<Node>,
-    pool: &'a NodePool<SetTypes<K, C>>,
-    path: Path<SetTypes<K, C>>,
+    pool: &'a NodePool<SetTypes<K>>,
+    path: Path<SetTypes<K>>,
 }
 
-impl<'a, K, C> Iterator for SetIter<'a, K, C>
+impl<'a, K> Iterator for SetIter<'a, K>
 where
     K: 'a + Copy,
-    C: 'a + Comparator<K>,
 {
     type Item = K;
 
@@ -365,16 +366,16 @@ mod test {
     #[test]
     fn node_size() {
         // check that nodes are cache line sized when keys are 32 bits.
-        type F = SetTypes<u32, ()>;
+        type F = SetTypes<u32>;
         assert_eq!(mem::size_of::<NodeData<F>>(), 64);
     }
 
     #[test]
     fn empty() {
-        let mut f = SetForest::<u32, ()>::new();
+        let mut f = SetForest::<u32>::new();
         f.clear();
 
-        let mut s = Set::<u32, ()>::new();
+        let mut s = Set::<u32>::new();
         assert!(s.is_empty());
         s.clear(&mut f);
         assert!(!s.contains(7, &f, &()));
@@ -394,8 +395,8 @@ mod test {
 
     #[test]
     fn simple_cursor() {
-        let mut f = SetForest::<u32, ()>::new();
-        let mut s = Set::<u32, ()>::new();
+        let mut f = SetForest::<u32>::new();
+        let mut s = Set::<u32>::new();
         let mut c = SetCursor::new(&mut s, &mut f, &());
 
         assert!(c.insert(50));
@@ -436,8 +437,8 @@ mod test {
 
     #[test]
     fn two_level_sparse_tree() {
-        let mut f = SetForest::<u32, ()>::new();
-        let mut s = Set::<u32, ()>::new();
+        let mut f = SetForest::<u32>::new();
+        let mut s = Set::<u32>::new();
         let mut c = SetCursor::new(&mut s, &mut f, &());
 
         // Insert enough elements that we get a two-level tree.
@@ -482,8 +483,8 @@ mod test {
 
     #[test]
     fn three_level_sparse_tree() {
-        let mut f = SetForest::<u32, ()>::new();
-        let mut s = Set::<u32, ()>::new();
+        let mut f = SetForest::<u32>::new();
+        let mut s = Set::<u32>::new();
         let mut c = SetCursor::new(&mut s, &mut f, &());
 
         // Insert enough elements that we get a 3-level tree.
@@ -535,7 +536,7 @@ mod test {
     // Level 4: 512 leafs, up to 7680 elements
     //
     // A 3-level tree can hold at most 960 elements.
-    fn dense4l(f: &mut SetForest<i32, ()>) -> Set<i32, ()> {
+    fn dense4l(f: &mut SetForest<i32>) -> Set<i32> {
         f.clear();
         let mut s = Set::new();
 
@@ -549,7 +550,7 @@ mod test {
 
     #[test]
     fn four_level() {
-        let mut f = SetForest::<i32, ()>::new();
+        let mut f = SetForest::<i32>::new();
         let mut s = dense4l(&mut f);
 
         assert_eq!(
@@ -593,7 +594,7 @@ mod test {
 
     #[test]
     fn four_level_clear() {
-        let mut f = SetForest::<i32, ()>::new();
+        let mut f = SetForest::<i32>::new();
         let mut s = dense4l(&mut f);
         s.clear(&mut f);
     }
diff --git a/lib/codegen/src/flowgraph.rs b/lib/codegen/src/flowgraph.rs
index 9eda2741af..b84da7cd0b 100644
--- a/lib/codegen/src/flowgraph.rs
+++ b/lib/codegen/src/flowgraph.rs
@@ -61,11 +61,11 @@ struct CFGNode {
     ///
     /// The redundant EBB stored here is always consistent with the CFG successor lists, even after
     /// the IR has been edited.
-    pub predecessors: bforest::Map<Inst, Ebb, ()>,
+    pub predecessors: bforest::Map<Inst, Ebb>,
 
     /// Set of EBBs that are the targets of branches and jumps in this EBB.
     /// The set is ordered by EBB number, indicated by the `()` comparator type.
-    pub successors: bforest::Set<Ebb, ()>,
+    pub successors: bforest::Set<Ebb>,
 }
 
 /// The Control Flow Graph maintains a mapping of ebbs to their predecessors
@@ -73,8 +73,8 @@ struct CFGNode {
 /// extended basic blocks.
 pub struct ControlFlowGraph {
     data: EntityMap<Ebb, CFGNode>,
-    pred_forest: bforest::MapForest<Inst, Ebb, ()>,
-    succ_forest: bforest::SetForest<Ebb, ()>,
+    pred_forest: bforest::MapForest<Inst, Ebb>,
+    succ_forest: bforest::SetForest<Ebb>,
     valid: bool,
 }
 
@@ -193,7 +193,7 @@ impl ControlFlowGraph {
 /// An iterator over EBB predecessors. The iterator type is `BasicBlock`.
 ///
 /// Each predecessor is an instruction that branches to the EBB.
-pub struct PredIter<'a>(bforest::MapIter<'a, Inst, Ebb, ()>);
+pub struct PredIter<'a>(bforest::MapIter<'a, Inst, Ebb>);
 
 impl<'a> Iterator for PredIter<'a> {
     type Item = BasicBlock;
@@ -204,7 +204,7 @@ impl<'a> Iterator for PredIter<'a> {
 }
 
 /// An iterator over EBB successors. The iterator type is `Ebb`.
-pub type SuccIter<'a> = bforest::SetIter<'a, Ebb, ()>;
+pub type SuccIter<'a> = bforest::SetIter<'a, Ebb>;
 
 #[cfg(test)]
 mod tests {
diff --git a/lib/codegen/src/regalloc/liverange.rs b/lib/codegen/src/regalloc/liverange.rs
index f330fb12b5..cc6a985641 100644
--- a/lib/codegen/src/regalloc/liverange.rs
+++ b/lib/codegen/src/regalloc/liverange.rs
@@ -112,6 +112,7 @@ use entity::SparseMapValue;
 use ir::{Ebb, ExpandedProgramPoint, Inst, Layout, ProgramOrder, ProgramPoint, Value};
 use regalloc::affinity::Affinity;
 use std::cmp::Ordering;
+use std::marker::PhantomData;
 
 /// Global live range of a single SSA value.
 ///
@@ -172,7 +173,9 @@ pub struct GenLiveRange<PO: ProgramOrder> {
     ///
     /// The entries are non-overlapping, and none of them overlap the EBB where the value is
     /// defined.
-    liveins: bforest::Map<Ebb, Inst, PO>,
+    liveins: bforest::Map<Ebb, Inst>,
+
+    po: PhantomData<*const PO>,
 }
 
 /// Context information needed to query a `LiveRange`.
@@ -180,14 +183,14 @@ pub struct LiveRangeContext<'a, PO: 'a + ProgramOrder> {
     /// Ordering of EBBs.
     pub order: &'a PO,
     /// Memory pool.
-    pub forest: &'a bforest::MapForest<Ebb, Inst, PO>,
+    pub forest: &'a bforest::MapForest<Ebb, Inst>,
 }
 
 impl<'a, PO: ProgramOrder> LiveRangeContext<'a, PO> {
     /// Make a new context.
     pub fn new(
         order: &'a PO,
-        forest: &'a bforest::MapForest<Ebb, Inst, PO>,
+        forest: &'a bforest::MapForest<Ebb, Inst>,
     ) -> LiveRangeContext<'a, PO> {
         LiveRangeContext { order, forest }
     }
@@ -205,11 +208,13 @@ impl<'a, PO: ProgramOrder> Clone for LiveRangeContext<'a, PO> {
 impl<'a, PO: ProgramOrder> Copy for LiveRangeContext<'a, PO> {}
 
 /// Forest of B-trees used for storing live ranges.
-pub type LiveRangeForest = bforest::MapForest<Ebb, Inst, Layout>;
+pub type LiveRangeForest = bforest::MapForest<Ebb, Inst>;
 
-impl<PO: ProgramOrder> bforest::Comparator<Ebb> for PO {
+struct Cmp<'a, PO: ProgramOrder + 'a>(&'a PO);
+
+impl<'a, PO: ProgramOrder> bforest::Comparator<Ebb> for Cmp<'a, PO> {
     fn cmp(&self, a: Ebb, b: Ebb) -> Ordering {
-        self.cmp(a, b)
+        self.0.cmp(a, b)
     }
 }
 
@@ -224,6 +229,7 @@ impl<PO: ProgramOrder> GenLiveRange<PO> {
             def_begin: def,
             def_end: def,
             liveins: bforest::Map::new(),
+            po: PhantomData,
         }
     }
 
@@ -243,7 +249,7 @@ impl<PO: ProgramOrder> GenLiveRange<PO> {
         ebb: Ebb,
         to: Inst,
         order: &PO,
-        forest: &mut bforest::MapForest<Ebb, Inst, PO>,
+        forest: &mut bforest::MapForest<Ebb, Inst>,
     ) -> bool {
         // First check if we're extending the def interval.
         //
@@ -264,7 +270,8 @@ impl<PO: ProgramOrder> GenLiveRange<PO> {
         }
 
         // Now check if we're extending any of the existing live-in intervals.
-        let mut c = self.liveins.cursor(forest, order);
+        let cmp = Cmp(order);
+        let mut c = self.liveins.cursor(forest, &cmp);
         let first_time_livein;
 
         if let Some(end) = c.goto(ebb) {
@@ -367,8 +374,9 @@ impl<PO: ProgramOrder> GenLiveRange<PO> {
     /// answer, but it is also possible that an even later program point is returned. So don't
     /// depend on the returned `Inst` to belong to `ebb`.
     pub fn livein_local_end(&self, ebb: Ebb, ctx: LiveRangeContext<PO>) -> Option<Inst> {
+        let cmp = Cmp(ctx.order);
         self.liveins
-            .get_or_less(ebb, ctx.forest, ctx.order)
+            .get_or_less(ebb, ctx.forest, &cmp)
             .and_then(|(_, inst)| {
                 // We have an entry that ends at `inst`.
                 if ctx.order.cmp(inst, ebb) == Ordering::Greater {
@@ -390,10 +398,7 @@ impl<PO: ProgramOrder> GenLiveRange<PO> {
     ///
     /// Note that the intervals are stored in a compressed form so each entry may span multiple
     /// EBBs where the value is live in.
-    pub fn liveins<'a>(
-        &'a self,
-        ctx: LiveRangeContext<'a, PO>,
-    ) -> bforest::MapIter<'a, Ebb, Inst, PO> {
+    pub fn liveins<'a>(&'a self, ctx: LiveRangeContext<'a, PO>) -> bforest::MapIter<'a, Ebb, Inst> {
         self.liveins.iter(ctx.forest)
     }
 
@@ -507,11 +512,7 @@ mod tests {
         }
 
         // Validate the live range invariants.
-        fn validate(
-            &self,
-            lr: &GenLiveRange<ProgOrder>,
-            forest: &bforest::MapForest<Ebb, Inst, ProgOrder>,
-        ) {
+        fn validate(&self, lr: &GenLiveRange<ProgOrder>, forest: &bforest::MapForest<Ebb, Inst>) {
             // The def interval must cover a single EBB.
             let def_ebb = self.pp_ebb(lr.def_begin);
             assert_eq!(def_ebb, self.pp_ebb(lr.def_end));