diff --git a/game/mode.fnl b/game/mode.fnl
index 6841292..1609a2f 100644
--- a/game/mode.fnl
+++ b/game/mode.fnl
@@ -6,18 +6,18 @@
 (local dim (require :game.dim))
 (local {: draw : update} (util.require :game.entity))
 
-(fn game-update [dt])
-
-(fn exception-update [dt]
+(fn exception-update []
   (when (love.keyboard.isDown :f2)
     (set state.update-exception nil)))
 
-(fn update [dt]
+(fn wrap-call [thunk]
   (if state.update-exception
-    (exception-update dt)
-    (xpcall #(game-update dt) (fn [msg]
+    (exception-update)
+    (xpcall thunk (fn [msg]
       (set state.update-exception (.. msg "\n" (debug.traceback)))))))
 
+(fn update [dt] (wrap-call #(rules.update dt)))
+
 (fn game-draw []
   (let [xnext (/ dim.tilesize 2)
         xwell (* dim.tilesize 5)
@@ -37,5 +37,10 @@
     (exception-draw)
     (game-draw)))
 
-{: update : draw}
+(fn handler [ev ...]
+  (let [f (. rules ev)
+        args [...]]
+    (when f (wrap-call #(f (table.unpack args))))))
+
+{: update : draw : handler}
 
diff --git a/game/rules.fnl b/game/rules.fnl
index 1057074..76fe437 100644
--- a/game/rules.fnl
+++ b/game/rules.fnl
@@ -2,6 +2,7 @@
 (local map (require :game.tilemap))
 (local tileset (require :game.tiles))
 (local state (require :game.state))
+(local helpers (require :game.helpers))
 
 (local Rules {})
 
@@ -78,7 +79,7 @@
     (. possible-values ivalue)))
 
 (fn Rules.tetromino [k irotation]
-  (let [rotations (or (. state.tetrominoes k) [["##" "##"]])
+  (let [rotations (or (. state.tetrominoes k) [])
         irotation (+ (% (- irotation 1) (length rotations)) 1)]
     (. rotations irotation)))
 
@@ -90,12 +91,12 @@
     (map.set-itile-at 11 y state.well "X"))
   (for [x 0 11]
     (map.set-itile-at x 20 state.well "X"))
-  (set state.drop-ms 750)
+  (set state.drop-speed-ms 750)
   (Rules.play-next-piece))
 
 (fn Rules.play-next-piece []
   (let [piece (or state.next-piece (Rules.choose-random-tetromino))
-        x (/ (- (length (. state.well 1)) 2) 2)]
+        x (math.floor (/ (- (length (. state.well 1)) 2) 2))]
     (set state.current {: piece : x :y 0 :irotation 1})
     (set state.next-piece (Rules.choose-random-tetromino))))
 
@@ -103,5 +104,73 @@
   (when state.current
     (Rules.tetromino state.current.piece state.current.irotation)))
 
+(fn solid-positions [tetromino ?x ?y]
+  (let [h (length tetromino)
+        w (length (. tetromino 1))
+        x (or ?x 0)
+        y (or ?y 0)]
+    (icollect [tx ty (helpers.all-coordinates w h)]
+      (let [itile (map.itile-at tx ty tetromino)]
+        (when (not= itile " ") [(+ x tx) (+ y ty) itile])))))
+
+(fn Rules.collides? [tetromino x y]
+  (var collides false)
+  (when tetromino
+    (each [_ [wx wy] (ipairs (solid-positions tetromino x y)) :until collides]
+      (set collides (not= (map.itile-at wx wy state.well) " "))))
+  collides)
+
+(fn Rules.place-piece [tetromino x y]
+  (each [_ [wx wy itile] (ipairs (solid-positions tetromino x y))]
+    (map.set-itile-at wx wy state.well itile)))
+
+(fn Rules.try-move-piece [dx dy]
+  (when state.current
+    (let [tetromino (Rules.current-tetromino)
+          x (+ state.current.x dx)
+          y (+ state.current.y dy)
+          stopped (Rules.collides? tetromino x y)]
+      (if (and stopped (not= dy 0)) ; dropping
+          (do (Rules.place-piece tetromino state.current.x state.current.y)
+              (Rules.play-next-piece))
+
+          (not stopped)
+          (do (set state.current.x x)
+              (set state.current.y y))))))
+
+(fn Rules.rotate [di]
+  (when state.current
+    (set state.current.irotation (+ state.current.irotation di))))
+
+(set Rules.commands
+  {:move Rules.try-move-piece
+   :rotate Rules.rotate
+   :reset Rules.reset-game})
+
+(set Rules.keymap
+  {:left  [:move -1 0]
+   :right [:move 1 0]
+   :down  [:move 0 1]
+   :up    [:rotate 1]
+   :z     [:rotate -1]
+   :x     [:rotate 1]
+   :r     [:reset]})
+
+(fn Rules.run-command [cmd]
+  (when cmd
+    (let [[command & args] cmd
+          f (. Rules.commands command)]
+      (when f (f (table.unpack args))))))
+
+(fn Rules.keypressed [key]
+  (Rules.run-command (. Rules.keymap key)))
+
+(fn Rules.update [dt]
+  (let [drop-ms (- (or state.drop-ms state.drop-speed-ms) (* dt 1000))]
+    (if (<= drop-ms 0)
+        (do (set state.drop-ms nil)
+            (Rules.try-move-piece 0 1))
+      (set state.drop-ms drop-ms))))
+
 Rules
 
diff --git a/lib/lume.lua b/lib/lume.lua
index 2157891..48c7a68 100644
--- a/lib/lume.lua
+++ b/lib/lume.lua
@@ -689,7 +689,7 @@ function lume.hotswap(modname)
   local oldglobal = lume.clone(_G)
   local updated = {}
   local function update(old, new)
-    if updated[old] then return end
+    if old == nil or updated[old] then return end
     updated[old] = true
     local oldmt, newmt = getmetatable(old), getmetatable(new)
     if oldmt and newmt then update(oldmt, newmt) end