diff --git a/src/libstd/map.rs b/src/libstd/map.rs
index 915202143a1ea..730b5275e1d79 100644
--- a/src/libstd/map.rs
+++ b/src/libstd/map.rs
@@ -27,7 +27,24 @@ pub trait Map<K:Eq IterBytes Hash Copy, V: Copy> {
      *
      * Returns true if the key did not already exist in the map
      */
-    fn insert(v: K, v: V) -> bool;
+    fn insert(key: K, value: V) -> bool;
+
+    /**
+     * Add a value to the map.
+     *
+     * If the map contains a value for the key, use the function
+     * to set a new value.
+     */
+    fn insert_with_key(key: K, newval: V, ff: fn(K, V, V) -> V) -> bool;
+
+    /**
+     * Add a value to the map.
+     *
+     * If the map contains a value for the key, use the function
+     * to set a new value.  (Like insert_with_key, but with a function
+     * of only values.)
+     */
+    fn insert_with(key: K, newval: V, ff: fn(V, V) -> V) -> bool;
 
     /// Returns true if the map contains a value for the specified key
     pure fn contains_key(key: K) -> bool;
@@ -264,6 +281,59 @@ pub mod chained {
             }
         }
 
+        fn insert_with_key(key: K, newval: V, ff: fn(K, V, V) -> V) -> bool {
+/*
+            match self.find(key) {
+                None            => return self.insert(key, val),
+                Some(copy orig) => return self.insert(key, ff(key, orig, val))
+            }
+*/
+
+            let hash = key.hash_keyed(0,0) as uint;
+            match self.search_tbl(&key, hash) {
+              NotFound => {
+                self.count += 1u;
+                let idx = hash % vec::len(self.chains);
+                let old_chain = self.chains[idx];
+                self.chains[idx] = Some(@Entry {
+                    hash: hash,
+                    key: key,
+                    value: newval,
+                    next: old_chain});
+
+                // consider rehashing if more 3/4 full
+                let nchains = vec::len(self.chains);
+                let load = {num: (self.count + 1u) as int,
+                            den: nchains as int};
+                if !util::rational_leq(load, {num:3, den:4}) {
+                    self.rehash();
+                }
+
+                return true;
+              }
+              FoundFirst(idx, entry) => {
+                self.chains[idx] = Some(@Entry {
+                    hash: hash,
+                    key: key,
+                    value: ff(key, entry.value, newval),
+                    next: entry.next});
+                return false;
+              }
+              FoundAfter(prev, entry) => {
+                prev.next = Some(@Entry {
+                    hash: hash,
+                    key: key,
+                    value: ff(key, entry.value, newval),
+                    next: entry.next});
+                return false;
+              }
+            }
+        }
+
+        fn insert_with(key: K, newval: V, ff: fn(V, V) -> V) -> bool {
+            return self.insert_with_key(key, newval, |_k, v, v1| ff(v,v1));
+        }
+
         pure fn get(k: K) -> V {
             let opt_v = self.find(k);
             if opt_v.is_none() {
@@ -447,6 +517,17 @@ impl<K: Eq IterBytes Hash Copy, V: Copy> @Mut<LinearMap<K, V>>:
         }
     }
 
+    fn insert_with_key(key: K, newval: V, ff: fn(K, V, V) -> V) -> bool {
+        match self.find(key) {
+            None            => return self.insert(key, newval),
+            Some(copy orig) => return self.insert(key, ff(key, orig, newval))
+        }
+    }
+
+    fn insert_with(key: K, newval: V, ff: fn(V, V) -> V) -> bool {
+        return self.insert_with_key(key, newval, |_k, v, v1| ff(v,v1));
+    }
+
     fn remove(key: K) -> bool {
         do self.borrow_mut |p| {
             p.remove(&key)
@@ -750,4 +831,35 @@ mod tests {
         assert map.get(~"b") == 2;
         assert map.get(~"c") == 3;
     }
+
+    #[test]
+    fn test_insert_with_key() {
+        let map = map::HashMap::<~str, uint>();
+
+        // given a new key, initialize it with this new count, given
+        // given an existing key, add more to its count
+        fn addMoreToCount(_k: ~str, v0: uint, v1: uint) -> uint {
+            v0 + v1
+        }
+
+        fn addMoreToCount_simple(v0: uint, v1: uint) -> uint {
+            v0 + v1
+        }
+
+        // count the number of several types of animal,
+        // adding in groups as we go
+        map.insert_with(~"cat",      1, addMoreToCount_simple);
+        map.insert_with_key(~"mongoose", 1, addMoreToCount);
+        map.insert_with(~"cat",      7, addMoreToCount_simple);
+        map.insert_with_key(~"ferret",   3, addMoreToCount);
+        map.insert_with_key(~"cat",      2, addMoreToCount);
+
+        // check the total counts
+        assert 10 == option::get(map.find(~"cat"));
+        assert  3 == option::get(map.find(~"ferret"));
+        assert  1 == option::get(map.find(~"mongoose"));
+
+        // sadly, no mythical animals were counted!
+        assert None == map.find(~"unicorn");
+    }
 }
diff --git a/src/libstd/smallintmap.rs b/src/libstd/smallintmap.rs
index 9dc216a21557a..2fdfa3deea856 100644
--- a/src/libstd/smallintmap.rs
+++ b/src/libstd/smallintmap.rs
@@ -103,6 +103,17 @@ impl<V: Copy> SmallIntMap<V>: map::Map<uint, V> {
     pure fn find(key: uint) -> Option<V> { find(self, key) }
     fn rehash() { fail }
 
+    fn insert_with_key(key: uint, val: V, ff: fn(uint, V, V) -> V) -> bool {
+        match self.find(key) {
+            None            => return self.insert(key, val),
+            Some(copy orig) => return self.insert(key, ff(key, orig, val)),
+        }
+    }
+
+    fn insert_with(key: uint, newval: V, ff: fn(V, V) -> V) -> bool {
+        return self.insert_with_key(key, newval, |_k, v, v1| ff(v,v1));
+    }
+
     pure fn each(it: fn(key: uint, value: V) -> bool) {
         self.each_ref(|k, v| it(*k, *v))
     }
@@ -142,3 +153,37 @@ impl<V: Copy> SmallIntMap<V>: ops::Index<uint, V> {
 pub fn as_map<V: Copy>(s: SmallIntMap<V>) -> map::Map<uint, V> {
     s as map::Map::<uint, V>
 }
+
+#[cfg(test)]
+mod tests {
+
+    #[test]
+    fn test_insert_with_key() {
+        let map: SmallIntMap<uint> = mk();
+
+        // given a new key, initialize it with this new count, given
+        // given an existing key, add more to its count
+        fn addMoreToCount(_k: uint, v0: uint, v1: uint) -> uint {
+            v0 + v1
+        }
+
+        fn addMoreToCount_simple(v0: uint, v1: uint) -> uint {
+            v0 + v1
+        }
+
+        // count integers
+        map.insert_with(3, 1, addMoreToCount_simple);
+        map.insert_with_key(9, 1, addMoreToCount);
+        map.insert_with(3, 7, addMoreToCount_simple);
+        map.insert_with_key(5, 3, addMoreToCount);
+        map.insert_with_key(3, 2, addMoreToCount);
+
+        // check the total counts
+        assert 10 == option::get(map.find(3));
+        assert  3 == option::get(map.find(5));
+        assert  1 == option::get(map.find(9));
+
+        // sadly, no sevens were counted
+        assert None == map.find(7);
+    }
+}
diff --git a/src/test/bench/shootout-k-nucleotide-pipes.rs b/src/test/bench/shootout-k-nucleotide-pipes.rs
index bf94e11980a60..8030ca2672175 100644
--- a/src/test/bench/shootout-k-nucleotide-pipes.rs
+++ b/src/test/bench/shootout-k-nucleotide-pipes.rs
@@ -69,10 +69,7 @@ fn find(mm: HashMap<~[u8], uint>, key: ~str) -> uint {
 // given a map, increment the counter for a key
 fn update_freq(mm: HashMap<~[u8], uint>, key: &[u8]) {
     let key = vec::slice(key, 0, key.len());
-    match mm.find(key) {
-      option::None      => { mm.insert(key, 1u      ); }
-      option::Some(val) => { mm.insert(key, 1u + val); }
-    }
+    mm.insert_with(key, 1, |v,v1| { v+v1 });
 }
 
 // given a ~[u8], for each window call a function
diff --git a/src/test/bench/shootout-k-nucleotide.rs b/src/test/bench/shootout-k-nucleotide.rs
index 9bc7abfdff78e..8efe3c7575fb7 100644
--- a/src/test/bench/shootout-k-nucleotide.rs
+++ b/src/test/bench/shootout-k-nucleotide.rs
@@ -66,10 +66,7 @@ fn find(mm: HashMap<~[u8], uint>, key: ~str) -> uint {
 // given a map, increment the counter for a key
 fn update_freq(mm: HashMap<~[u8], uint>, key: &[u8]) {
     let key = vec::slice(key, 0, key.len());
-    match mm.find(key) {
-      option::None      => { mm.insert(key, 1u      ); }
-      option::Some(val) => { mm.insert(key, 1u + val); }
-    }
+    mm.insert_with(key, 1, |v,v1| { v+v1 });
 }
 
 // given a ~[u8], for each window call a function
diff --git a/src/test/run-pass/class-impl-very-parameterized-trait.rs b/src/test/run-pass/class-impl-very-parameterized-trait.rs
index c11e41eb57f46..ad7be9d86da79 100644
--- a/src/test/run-pass/class-impl-very-parameterized-trait.rs
+++ b/src/test/run-pass/class-impl-very-parameterized-trait.rs
@@ -61,6 +61,21 @@ impl<T: Copy> cat<T> : Map<int, T> {
      else { None }
   }
 
+  fn insert_with_key(+key: int, +val: T, ff: fn(+k: int, +v0: T, +v1: T) -> T) -> bool {
+    match self.find(key) {
+      None            => return self.insert(key, val),
+      Some(copy orig) => return self.insert(key, ff(key, orig, val))
+    }
+  }
+
+  fn insert_with(+key: int, +val: T, ff: fn(+v0: T, +v1: T) -> T) -> bool {
+    match self.find(key) {
+      None            => return self.insert(key, val),
+      Some(copy orig) => return self.insert(key, ff(orig, val))
+    }
+  }
+
+
   fn remove(+k:int) -> bool {
     match self.find(k) {
       Some(x) => {