diff --git a/pixie/stdlib.pxi b/pixie/stdlib.pxi
index 6c908a82..6070f410 100644
--- a/pixie/stdlib.pxi
+++ b/pixie/stdlib.pxi
@@ -3110,3 +3110,15 @@ ex: (vary-meta x assoc :foo 42)"
    :added "0.1"}
   [f x]
   (->Iterate f x))
+
+(defn compare-and-set! 
+  {:doc "Atomically sets the value of the atom to newval iff the current value of atom is oldval. 
+         Returns true if reset happens, else false."
+   :signatures [[atom oldval newval]]
+   :added "0.2"}
+  [atom oldval newval]
+  (if (= @atom oldval)
+    (do
+      (reset! atom newval)
+      true)
+    false)
diff --git a/pixie/vm/atom.py b/pixie/vm/atom.py
index 28254673..e21f2dfe 100644
--- a/pixie/vm/atom.py
+++ b/pixie/vm/atom.py
@@ -13,18 +13,28 @@ def with_meta(self, meta):
     def meta(self):
         return self._meta
 
-    def __init__(self, boxed_value, meta=nil):
+    def with_watch(self, watch_key, watch_fn):
+        return Atom(self._boxed_value,
+                    self._meta,
+                    watch_key,
+                    watch_fn)
+    
+    def __init__(self, boxed_value, 
+                 meta=nil,
+                 watch_key=nil, watch_fn=nil):
         self._boxed_value = boxed_value
         self._meta = meta
-
+        self._watch_key = watch_key
+        self._watch_fn = watch_fn
 
 @extend(proto._reset_BANG_, Atom)
 def _reset(self, v):
     assert isinstance(self, Atom)
+    if self._watch_fn is not nil:
+        self._watch_fn.invoke([self._watch_key, self, self._boxed_value, v])
     self._boxed_value = v
     return v
 
-
 @extend(proto._deref, Atom)
 def _deref(self):
     assert isinstance(self, Atom)
@@ -40,6 +50,11 @@ def _with_meta(self, meta):
     assert isinstance(self, Atom)
     return self.with_meta(meta)
 
+@extend(proto._with_watch, Atom)
+def _with_watch(self, watch_key, watch_fn):
+    assert isinstance(self, Atom)
+    return self.with_watch(watch_key, watch_fn)
+
 @as_var("atom")
 def atom(val=nil):
     return Atom(val)
diff --git a/pixie/vm/stdlib.py b/pixie/vm/stdlib.py
index d8611d72..ed8a49d6 100644
--- a/pixie/vm/stdlib.py
+++ b/pixie/vm/stdlib.py
@@ -63,6 +63,9 @@
 
 defprotocol("pixie.stdlib", "IMessageObject", ["-call-method", "-get-attr"])
 
+defprotocol("pixie.stdlib", "IWatch", ["-with-watch"])
+defprotocol("pixie.stdlib", "IValidate", ["-with-validator"])
+
 def maybe_mark_finalizer(self, tp):
     if self is _finalize_BANG_:
         print "MARKING ", tp
@@ -278,6 +281,10 @@ def __meta(a):
 def __with_meta(a, b):
     return rt._with_meta(a, b)
 
+@as_var("with-watch")
+def __with_watch(a, b, c):
+    return rt._with_watch(a, b, c)
+
 @returns(bool)
 @as_var("has-meta?")
 def __has_meta(a):