diff --git a/examples/benchmark_n-body.carp b/examples/benchmark_n-body.carp
index d1b871ef..872af10f 100644
--- a/examples/benchmark_n-body.carp
+++ b/examples/benchmark_n-body.carp
@@ -52,15 +52,15 @@
 (defn reduce-pz [t b] (+ @t (* (Planet.vz b) (Planet.mass b))))
 
 (defn offset_momentum [bodies]
-  (let [b (first bodies)
+  (let [b (nth bodies 0)
         px (reduce reduce-px 0.0 bodies)
         py (reduce reduce-py 0.0 bodies)
         pz (reduce reduce-pz 0.0 bodies)]
-    (aset! bodies 0 
-      (=> b
-        (Planet.set-vx (/ (neg px) (solar_mass)))
-        (Planet.set-vy (/ (neg py) (solar_mass)))
-        (Planet.set-vz (/ (neg pz) (solar_mass)))))))
+    (do 
+      (Planet.set!-vx b (/ (neg px) (solar_mass)))
+      (Planet.set!-vy b (/ (neg py) (solar_mass)))
+      (Planet.set!-vz b (/ (neg pz) (solar_mass))))))
+
 
 
 (defn energy [bodies]
@@ -84,35 +84,30 @@
 
 (defn update-planet [i bodies dt]
   (let [b (nth bodies i)]
-    (aset! bodies i 
-      (=> @b
-        (Planet.set-x (+ (Planet.x b) (* dt (Planet.vx b))))
-        (Planet.set-y (+ (Planet.y b) (* dt (Planet.vy b))))
-        (Planet.set-z (+ (Planet.z b) (* dt (Planet.vz b))))))))
+    (do
+      (Planet.set!-x b (+ (Planet.x b) (* dt (Planet.vx b))))
+      (Planet.set!-y b (+ (Planet.y b) (* dt (Planet.vy b))))
+      (Planet.set!-z b (+ (Planet.z b) (* dt (Planet.vz b)))))))
 
 (defn advance [bodies dt]
   (do
     (for [i 0 (count bodies)]
       (let [b (nth bodies i)]
         (for [j (+ i 1) (count bodies)]
-          (let-do [b2 (nth bodies j)
+          (let [b2 (nth bodies j)
                 dx (- (Planet.x b) (Planet.x b2))
                 dy (- (Planet.y b) (Planet.y b2))
                 dz (- (Planet.z b) (Planet.z b2))
                 dist (sqrt (+ (ipow dx 2) (+ (ipow dy 2) (ipow dz 2))))
                 mag (/ dt (ipow dist 3))]
-
-
-            (aset! bodies i 
-              (=> @b
-                (Planet.set-vx (- (Planet.vx b) (* dx (* (Planet.mass b2) mag))))
-                (Planet.set-vy (- (Planet.vy b) (* dy (* (Planet.mass b2) mag))))
-                (Planet.set-vz (- (Planet.vz b) (* dz (* (Planet.mass b2) mag))))))
-            (aset! bodies j 
-              (=> @b2
-                (Planet.set-vx (+ (Planet.vx b2) (* dx (* (Planet.mass b) mag))))
-                (Planet.set-vy (+ (Planet.vy b2) (* dy (* (Planet.mass b) mag))))
-                (Planet.set-vz (+ (Planet.vz b2) (* dz (* (Planet.mass b) mag))))))))))
+            (do
+              (Planet.set!-vx b (- (Planet.vx b) (* dx (* (Planet.mass b2) mag))))
+              (Planet.set!-vy b (- (Planet.vy b) (* dy (* (Planet.mass b2) mag))))
+              (Planet.set!-vz b (- (Planet.vz b) (* dz (* (Planet.mass b2) mag))))
+                
+              (Planet.set!-vx b2 (+ (Planet.vx b2) (* dx (* (Planet.mass b) mag))))
+              (Planet.set!-vy b2 (+ (Planet.vy b2) (* dy (* (Planet.mass b) mag))))
+              (Planet.set!-vz b2 (+ (Planet.vz b2) (* dz (* (Planet.mass b) mag)))))))))
 
     (for [i 0 (count bodies)]
       (update-planet i bodies dt))))
diff --git a/src/Deftype.hs b/src/Deftype.hs
index 24aa34cb..4a43769d 100644
--- a/src/Deftype.hs
+++ b/src/Deftype.hs
@@ -154,6 +154,7 @@ templatesForSingleMember typeEnv env insidePath structTy@(StructTy typeName _) (
       fixedMemberTy = if isManaged typeEnv t then RefTy t else t
   in [instanceBinderWithDeps (SymPath insidePath memberName) (FuncTy [RefTy p] fixedMemberTy) (templateGetter (mangle memberName) fixedMemberTy)
      ,instanceBinderWithDeps (SymPath insidePath ("set-" ++ memberName)) (FuncTy [p, t] p) (templateSetter typeEnv env (mangle memberName) t)
+     ,instanceBinderWithDeps (SymPath insidePath ("set!-" ++ memberName)) (FuncTy [RefTy (p), t] UnitTy) (templateSetterRef typeEnv env (mangle memberName) t)
      ,instanceBinderWithDeps (SymPath insidePath ("update-" ++ memberName))
                                                             (FuncTy [p, FuncTy [t] t] p)
                                                             (templateUpdater (mangle memberName))]
@@ -306,6 +307,20 @@ templateSetter typeEnv env memberName memberTy =
            then depsOfPolymorphicFunction typeEnv env [] "delete" (typesDeleterFunctionType memberTy)
            else [])
 
+-- | The template for setters of a deftype.
+templateSetterRef :: TypeEnv -> Env -> String -> Ty -> Template
+templateSetterRef typeEnv env memberName memberTy =
+  Template
+    (FuncTy [RefTy (VarTy "p"), VarTy "t"] UnitTy)
+    (const (toTemplate "void $NAME($p* pRef, $t newValue)"))
+    (const (toTemplate (unlines ["$DECL {"
+                                ,"    pRef->" ++ memberName ++ " = newValue;"
+                                ,"}\n"])))
+    (\_ -> if isManaged typeEnv memberTy
+           then depsOfPolymorphicFunction typeEnv env [] "delete" (typesDeleterFunctionType memberTy)
+           else [])
+
+
 -- | The template for updater functions of a deftype
 -- | (allows changing a variable by passing an transformation function).
 templateUpdater :: String -> Template