diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6c343570..4b0895a4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,11 +12,14 @@ we support - while secretly sneaking in some performance upgrades. Enjoy!
 - [choo-handbook/upgrading/4.0.0]()
 
 ### changes
-- slim down server side rendering API |
+- :exclamation: slim down server side rendering API |
   [issue](https://github.com/yoshuawuyts/choo/issues/191) |
   [pull-request](https://github.com/yoshuawuyts/choo/pull/203)
-- update router API to be lisp-like | [issue]() | [pull-request]()
-- update `router` to use thunking |
+- :exclamation: update router API to be lisp-like | [issue]() |
+  [pull-request]()
+- :exclamation: swap `state` and `data` argument order |
+  [issue](https://github.com/yoshuawuyts/choo/issues/179)
+- update `router` to use memoization |
   [issue](https://github.com/yoshuawuyts/sheet-router/issues/17) |
   [pull-request](https://github.com/yoshuawuyts/sheet-router/pull/34)
 - support inline anchor links |
@@ -27,8 +30,6 @@ we support - while secretly sneaking in some performance upgrades. Enjoy!
 - update router API to handle hashes by default
 - update `location` state to expose `search` parameters (query strings) |
   [issue](https://github.com/yoshuawuyts/sheet-router/issues/31)
-- swap `state` and `data` argument order |
-  [issue](https://github.com/yoshuawuyts/choo/issues/179)
 
 ## `3.2.0`
 Wooh, `plugins` are a first class citizen now thanks to the `.use()` API. It's
diff --git a/README.md b/README.md
index a1bd018e..2fb0cc02 100644
--- a/README.md
+++ b/README.md
@@ -129,7 +129,7 @@ const app = choo()
 app.model({
   state: { title: 'Not quite set yet' },
   reducers: {
-    update: (data, state) => ({ title: data })
+    update: (state, data) => ({ title: data })
   }
 })
 
@@ -252,7 +252,7 @@ app.model({
   namespace: 'todos',
   state: { items: [] },
   reducers: {
-    add: (data, state) => ({ items: state.items.concat(data.payload) })
+    add: (state, data) => ({ items: state.items.concat(data.payload) })
   }
 })
 ```
@@ -297,7 +297,7 @@ app.model({
   namespace: 'todos',
   state: { items: [] },
   effects: {
-    addAndSave: (data, state, send, done) => {
+    addAndSave: (state, data, send, done) => {
       http.post('/todo', {body: data.payload, json: true}, (err, res, body) => {
         data.payload.id = body.id
         send('todos:add', data, done)
@@ -305,7 +305,7 @@ app.model({
     }
   },
   reducers: {
-    add: (data, state) => ({ items: state.items.concat(data.payload) })
+    add: (state, data) => ({ items: state.items.concat(data.payload) })
   }
 })
 ```
@@ -337,7 +337,7 @@ app.model({
     }
   ],
   effects: {
-    print: (data, state) => console.log(data.payload)
+    print: (state, data) => console.log(data.payload)
   }
 })
 ```
@@ -448,9 +448,9 @@ arguments:
   and handlers in other models
 - __state:__ initial values of `state` inside the model
 - __reducers:__ synchronous operations that modify state. Triggered by
-  `actions`. Signature of `(data, state)`.
+  `actions`. Signature of `(state, data)`.
 - __effects:__ asynchronous operations that don't modify state directly.
-  Triggered by `actions`, can call `actions`. Signature of `(data, state,
+  Triggered by `actions`, can call `actions`. Signature of `(state, data,
   send, done)`
 - __subscriptions:__ asynchronous read-only operations that don't modify state
   directly. Can call `actions`. Signature of `(send, done)`.
@@ -490,9 +490,9 @@ There are several `hooks` that are picked up by `choo`:
 - __onError(err, state, createSend):__ called when an `effect` or
   `subscription` emit an error. If no handler is passed, the default handler
   will `throw` on each error.
-- __onAction(action, state, name, caller, createSend):__ called when an
+- __onAction(state, data, name, caller, createSend):__ called when an
   `action` is fired.
-- __onStateChange(action, state, prev, caller, createSend):__ called after a
+- __onStateChange(state, data, prev, caller, createSend):__ called after a
   reducer changes the `state`.
 
 __:warning: Warning :warning:: plugins should only be used as a last resort.
diff --git a/examples/async-counter/client.js b/examples/async-counter/client.js
index 03539d26..71cce36f 100644
--- a/examples/async-counter/client.js
+++ b/examples/async-counter/client.js
@@ -8,14 +8,14 @@ app.model({
     counter: 0
   },
   reducers: {
-    increment: (data, state) => ({ counter: state.counter + 1 }),
-    decrement: (data, state) => ({ counter: state.counter - 1 })
+    increment: (state, data) => ({ counter: state.counter + 1 }),
+    decrement: (state, data) => ({ counter: state.counter - 1 })
   },
   effects: {
-    incrementAsync: function (data, state, send, done) {
+    incrementAsync: function (state, data, send, done) {
       setTimeout(() => send('increment', done), 1000)
     },
-    decrementAsync: function (data, state, send, done) {
+    decrementAsync: function (state, data, send, done) {
       setTimeout(() => send('decrement', done), 1000)
     }
   }
diff --git a/examples/http/client.js b/examples/http/client.js
index 69e4569e..b2c92ed5 100644
--- a/examples/http/client.js
+++ b/examples/http/client.js
@@ -11,12 +11,12 @@ const app = choo({
     const send = createSend('onError: ')
     send('app:error', err)
   },
-  onAction: function (data, state, name, caller, createSend) {
+  onAction: function (state, data, name, caller, createSend) {
     console.groupCollapsed(`Action: ${caller} -> ${name}`)
     console.log(data)
     console.groupEnd()
   },
-  onStateChange: function (data, state, prev, createSend) {
+  onStateChange: function (state, data, prev, createSend) {
     console.groupCollapsed('State')
     console.log(prev)
     console.log(state)
diff --git a/examples/http/models/api.js b/examples/http/models/api.js
index 9fd58263..5d9067a3 100644
--- a/examples/http/models/api.js
+++ b/examples/http/models/api.js
@@ -6,13 +6,13 @@ module.exports = {
     title: 'Button pushing machine 3000'
   },
   reducers: {
-    set: (data, state) => ({ 'title': data })
+    set: (state, data) => ({ 'title': data })
   },
   effects: {
-    good: function (data, state, send, done) {
+    good: function (state, data, send, done) {
       request('/good', send, done)
     },
-    bad: (data, state, send, done) => request('/bad', send, done)
+    bad: (state, data, send, done) => request('/bad', send, done)
   }
 }
 
diff --git a/examples/http/models/error.js b/examples/http/models/error.js
index bd1620a4..4530791b 100644
--- a/examples/http/models/error.js
+++ b/examples/http/models/error.js
@@ -15,13 +15,13 @@ module.exports = {
     triggerTime: null
   },
   reducers: {
-    setError: function (data, state) {
+    setError: function (state, data) {
       return {
         errors: state.errors.concat(data.message),
         errorTimeDone: data.errorTimeDone
       }
     },
-    'delError': function (data, state) {
+    'delError': function (state, data) {
       state.errors.shift()
       return { errors: state.errors }
     }
diff --git a/examples/sse/client.js b/examples/sse/client.js
index 1888cf46..0552fe40 100644
--- a/examples/sse/client.js
+++ b/examples/sse/client.js
@@ -33,16 +33,16 @@ function createModel () {
       }
     ],
     reducers: {
-      'print': (data, state) => {
+      'print': (state, data) => {
         return ({ msg: state.msg + ' ' + data.payload })
       }
     },
     effects: {
-      close: (data, state, send, done) => {
+      close: (state, data, send, done) => {
         stream.close()
         done()
       },
-      error: (data, state, send, done) => {
+      error: (state, data, send, done) => {
         console.error(`error: ${data.payload}`)
         done()
       }
diff --git a/examples/stopwatch/models/stopwatch.js b/examples/stopwatch/models/stopwatch.js
index cb540710..dec45543 100644
--- a/examples/stopwatch/models/stopwatch.js
+++ b/examples/stopwatch/models/stopwatch.js
@@ -8,14 +8,14 @@ module.exports = {
     laps: []
   },
   reducers: {
-    start: (data, state) => ({ start: true, startTime: Date.now() - state.elapsed }),
-    stop: (data, state) => ({ start: false }),
-    update: (data, state) => ({ elapsed: data }),
-    reset: (data, state) => ({ startTime: Date.now(), elapsed: 0, laps: [] }),
-    add: (data, state) => ({ laps: state.laps.concat(data) })
+    start: (state, data) => ({ start: true, startTime: Date.now() - state.elapsed }),
+    stop: (state, data) => ({ start: false }),
+    update: (state, data) => ({ elapsed: data }),
+    reset: (state, data) => ({ startTime: Date.now(), elapsed: 0, laps: [] }),
+    add: (state, data) => ({ laps: state.laps.concat(data) })
   },
   effects: {
-    now: (data, state, send, done) => {
+    now: (state, data, send, done) => {
       if (state.start) {
         let elapsed = data - state.startTime
         send('update', elapsed, done)
diff --git a/examples/title/client.js b/examples/title/client.js
index c04ea759..41bb0ff5 100644
--- a/examples/title/client.js
+++ b/examples/title/client.js
@@ -8,10 +8,10 @@ app.model({
     title: 'my demo app'
   },
   reducers: {
-    update: (data, state) => ({ title: data.payload })
+    update: (state, data) => ({ title: data.payload })
   },
   effects: {
-    update: (data, state, send, done) => {
+    update: (state, data, send, done) => {
       document.title = data.payload
       done()
     }
diff --git a/examples/vanilla/index.html b/examples/vanilla/index.html
index 63875ed1..72dcd718 100644
--- a/examples/vanilla/index.html
+++ b/examples/vanilla/index.html
@@ -12,8 +12,8 @@
         namespace: 'counter',
         state: { count: 0 },
         reducers: {
-          increment: (data, state) => ({count: state.count + 1}),
-          decrement: (data, state) => ({count: state.count - 1})
+          increment: (state, data) => ({count: state.count + 1}),
+          decrement: (state, data) => ({count: state.count - 1})
         }
       })
 
diff --git a/index.js b/index.js
index 4b41db99..ff68287b 100644
--- a/index.js
+++ b/index.js
@@ -70,7 +70,7 @@ function choo (opts) {
 
   // update the DOM after every state mutation
   // (obj, obj, obj, str, fn) -> null
-  function render (data, state, prev, name, createSend) {
+  function render (state, data, prev, name, createSend) {
     if (!_frame) {
       _frame = nanoraf(function (state, prev) {
         const newTree = _router(state.location.pathname, state, prev)
diff --git a/package.json b/package.json
index add750c7..1ebb34b6 100644
--- a/package.json
+++ b/package.json
@@ -36,7 +36,7 @@
   ],
   "license": "MIT",
   "dependencies": {
-    "barracks": "^8.1.1",
+    "barracks": "^9.0.0",
     "document-ready": "~1.0.2",
     "global": "^4.3.0",
     "hash-match": "^1.0.2",
@@ -58,7 +58,7 @@
     "es2020": "^1.0.1",
     "geval": "~2.1.1",
     "gzip-size-cli": "^1.0.0",
-    "insert-css": "^0.2.0",
+    "insert-css": "^1.0.0",
     "istanbul": "^0.4.4",
     "min-document": "~2.18.0",
     "pretty-bytes-cli": "^1.0.0",
diff --git a/tests/browser/basic.js b/tests/browser/basic.js
index b67e6bee..087310d8 100644
--- a/tests/browser/basic.js
+++ b/tests/browser/basic.js
@@ -17,16 +17,16 @@ test('state is immutable', function (t) {
     state: state,
     namespace: 'test',
     reducers: {
-      'no-reducer-mutate': (action, state) => {
+      'no-reducer-mutate': (state, data) => {
         return {}
       },
-      'mutate-on-return': (action, state) => {
-        delete action.type
-        return action
+      'mutate-on-return': (state, data) => {
+        delete data.type
+        return data
       }
     },
     effects: {
-      'triggers-reducers': (action, state, send, done) => {
+      'triggers-reducers': (state, data, send, done) => {
         send('test:mutate-on-return', {beep: 'barp'}, done)
       }
     }
diff --git a/tests/browser/hooks.js b/tests/browser/hooks.js
index 8e2faab2..80de35bf 100644
--- a/tests/browser/hooks.js
+++ b/tests/browser/hooks.js
@@ -10,16 +10,16 @@ test('hooks', function (t) {
     onError: function (err) {
       t.equal(err.message, 'effect error', 'onError: receives err')
     },
-    onAction: function (action, state, name, caller, createSend) {
+    onAction: function (state, data, name, caller, createSend) {
       if (name === 'explodes') return
-      t.deepEqual(action, {foo: 'bar'}, 'onAction: action data')
+      t.deepEqual(data, {foo: 'bar'}, 'onAction: action data')
       t.equal(state.clicks, 0, 'onAction: current state: 0 clicks')
-      t.equal(name, 'click', 'onAction: action name')
+      t.equal(name, 'click', 'onAction: data name')
       t.equal(caller, 'view: /', 'onAction: caller name')
       t.equal(typeof createSend, 'function', 'onAction: createSend fn')
     },
-    onStateChange: function (action, state, prev, createSend) {
-      t.deepEqual(action, {foo: 'bar'}, 'onState: action data')
+    onStateChange: function (state, data, prev, createSend) {
+      t.deepEqual(data, {foo: 'bar'}, 'onState: action data')
       t.deepEqual(state.clicks, 1, 'onState: new state: 1 clicks')
       t.deepEqual(prev.clicks, 0, 'onState: prev state: 0 clicks')
     }
@@ -30,10 +30,10 @@ test('hooks', function (t) {
       clicks: 0
     },
     reducers: {
-      click: (action, state) => ({clicks: state.clicks + 1})
+      click: (state, data) => ({clicks: state.clicks + 1})
     },
     effects: {
-      explodes: (action, state, send, done) => {
+      explodes: (state, data, send, done) => {
         setTimeout(() => done(new Error('effect error')), 5)
       }
     }
diff --git a/tests/browser/routing.js b/tests/browser/routing.js
index b1b12a95..4ef2c17b 100644
--- a/tests/browser/routing.js
+++ b/tests/browser/routing.js
@@ -6,7 +6,7 @@ const view = require('../../html')
 
 test('routing', function (t) {
   t.test('history', function (t) {
-    t.plan(3)
+    t.plan(2)
 
     const history = Event()
     const choo = proxyquire('../..', {
@@ -20,11 +20,11 @@ test('routing', function (t) {
         user: null
       },
       reducers: {
-        set: (action, state) => ({user: action.id})
+        set: (state, data) => ({user: data.id})
       },
       effects: {
-        open: function (action, state, send, done) {
-          t.deepEqual(action, {id: 1})
+        open: function (state, data, send, done) {
+          t.deepEqual(data, {id: 1})
           send('set', {id: 1}, function (err) {
             if (err) return done(err)
             history.broadcast('/users/1')
@@ -75,10 +75,10 @@ test('routing', function (t) {
   //       user: null
   //     },
   //     reducers: {
-  //       set: (action, state) => ({user: action.id})
+  //       set: (state, data) => ({user: action.id})
   //     },
   //     effects: {
-  //       open: function (action, state, send, done) {
+  //       open: function (state, data, send, done) {
   //         send('set', {id: 1}, function (err) {
   //           if (err) return done(err)
   //           hash.broadcast('#users/1')