diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index fb6766f..ccc06a6 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -17,9 +17,9 @@ To test with a real GitHub repository, you'll need to create a test repository a
   - **Payload URL:** Use the full `*.ngrok.io`
   - **Secret:** `development`
   - **Which events would you like to trigger this webhook?:** Choose **Send me everything**.
-0. Create a `.probot` in your repo with:
+0. Create a `.probot.js` in your repo with:
 
-        on issues.opened then comment("Hello World! Your bot is working!");
+        on("issues.opened").comment("Hello World! Your bot is working!");
 
 0. Open a new issue. Your bot should post a comment (you may need to refresh to see it).
 
@@ -34,6 +34,8 @@ To test with a real GitHub repository, you'll need to create a test repository a
 
 ## Adding an action
 
+_**TODO:** This is out of date and will be updated after plugin API is settled._
+
 [Actions](docs/configuration.md#then) are called when a webhook is delivered and any conditions are met. For example, this configuration in `.probot` calls two actions when a new issue is opened:
 
 ```
@@ -77,6 +79,8 @@ That's it! You now have everything you need to implement an action. If you're lo
 
 ## Adding a condition
 
+_**TODO:** This is out of date and will be updated after plugin API is settled._
+
 [Conditions](docs/configuration.md#then) are called when a webhook is delivered and are used to determine if the actions should be called. For example, this configuration in `.probot` checks if an issue or pull request has a label before closing it:
 
 ```
diff --git a/README.md b/README.md
index 21b56ab..fda331f 100644
--- a/README.md
+++ b/README.md
@@ -12,9 +12,14 @@ _**Heads up!** The [demo integration](https://github.com/integration/probot-demo
 
 0. Go to the **[demo integration](https://github.com/integration/probot-demo)**, click **Install**, and then select an organization.
 0. Add @probot as a collaborator with write access on your repository.
-0. Create a `.probot` file in your repository with the following contents. See [Configuration](docs/configuration.md) for more information on what behaviors can be built.
+0. Create a `.probot.js` file in your repository with the following contents. See [Configuration](docs/configuration.md) for more information on what behaviors can be built.
 
-        on issues.opened
-        then comment("Hello @{{ sender.login }}. Thanks for inviting me to your project. Read more about [all the things I can help you with][config]. I can't wait to get started!\\n[config]: https://github.com/bkeepers/PRobot/blob/master/docs/configuration.md");
+        on("issues.opened").comment(`
+          Hello @{{ sender.login }}. Thanks for inviting me to your project.
+          Read more about [all the things I can help you with][config]. I can't
+          wait to get started!
+
+          [config]: https://github.com/bkeepers/PRobot/blob/master/docs/configuration.md
+        `);
 
 0. Open a new issue. @probot should post a comment (you may need to refresh to see it).
diff --git a/docs/configuration.md b/docs/configuration.md
index 677b8c1..106f82c 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -1,25 +1,25 @@
 # Configuration
 
-Behaviors are configured in a file called `.probot` in your repository.
+Workflows are configured in a file called `.probot.js` in your repository.
 
 ```
-# Auto-respond to new issues and pull requests
-on issues.opened or pull_request.opened
-then comment("Thanks for your contribution! Expect a reply within 48 hours.")
-and label(triage);
+// Auto-respond to new issues and pull requests
+on('issues.opened', 'pull_request.opened')
+  .comment('Thanks for your contribution! Expect a reply within 48 hours.')
+  .label('triage');
 
-# Auto-close new pull requests
-on pull_request.opened
-then comment("Sorry @{{ user.login }}, pull requests are not accepted on this repository.")
-and close;
+// Auto-close new pull requests
+on('pull_request.opened')
+  .comment('Sorry @{{ user.login }}, pull requests are not accepted on this repository.')
+  .close();
 ```
 
-## Behaviors
+## Workflows
 
-Behaviors are composed of:
+Workflows are composed of:
 
 - [`on`](#on) - webhook events to listen to
-- [`if`](#if) (optional) - conditions to determine if the actions should be performed.
+- [`filter`](#filter) (optional) - conditions to determine if the actions should be performed.
 - [`then`](#then) - actions to take in response to the event
 
 ### `on`
@@ -27,19 +27,19 @@ Behaviors are composed of:
 Specifies the type of GitHub [webhook event](https://developer.github.com/webhooks/#events) that this behavior applies to:
 
 ```
-on issues then…
+on('issues')
 ```
 
 You can also specify multiple events to trigger this behavior:
 
 ```
-on issues or pull_request then…
+on('issues', 'pull_request')
 ```
 
 Many events also have an `action` (e.g. `created` for the `issue` event), which can be referenced with dot notation:
 
 ```
-on issues.labeled or issues.unlabeled then…
+on('issues.labeled', 'issues.unlabeled')
 ```
 
 [Webhook events](https://developer.github.com/webhooks/#events) include:
@@ -69,48 +69,20 @@ on issues.labeled or issues.unlabeled then…
 
 TODO: document actions
 
-### `if`
+### `filter`
 
-Only preform the actions if theses conditions are met. Conditions can be [operations](#operations) or [functions](#functions)
-
-Attributes of the [webhook payload](https://developer.github.com/webhooks/#events) can be used in conditions using the `@` syntax.
+Only preform the actions if the function returns `true`. The `event` is passed as an argument to the function and attributes of the [webhook payload](https://developer.github.com/webhooks/#events).
 
 ```
-if @issue.body contains "- [ ]"
+.filter(event => event.payload.issue.body.includes("- [ ]"))
 ```
 
-#### Operations
-
-Operator            | Description                         | Example
---------------------|-------------------------------------|-----------------------------------
-`is`                | equal                               | `@sender.login is "hubot"`
-`is not`            | not equal                           | `@sender.login is not "hubot"`
-`contains`          | string contains a substring         | `@issue.body contains "- [ ]"`
-`does not contain`  | string does not contain a substring | `@issue.body does not contain "- [x]"`
-`matches`           | matches a regular expression        | `@issue.title matches "^\[?WIP\]?"`
-`does not match`    | does not match a regular expression | `@issue.title does not match "v\d+\.\d+"`
-`and`               | logical and                         | `labeled(bug) and @sender.login is "hubot"`
-`or`                | logical or                          | `labeled(bug) or labeled(defect)`
-`not`               | negate a condition                  | `not labeled(bug)`
-
-#### Functions
-
-##### `labeled`
-
-Test if the label was added.
-
-```
-if labeled(bug)
-```
-
-### `then`
-
 #### `comment`
 
 Comments can be posted in response to any event performed on an Issue or Pull Request. Comments use [mustache](https://mustache.github.io/) for templates and can use any data from the event payload.
 
 ```
-… then comment("Hey @{{ user.login }}, thanks for the contribution!");
+.comment("Hey @{{ user.login }}, thanks for the contribution!");
 ```
 
 #### `close`
@@ -118,7 +90,7 @@ Comments can be posted in response to any event performed on an Issue or Pull Re
 Close an issue or pull request.
 
 ```
-… then close;
+.close();
 ```
 
 #### `open`
@@ -126,7 +98,7 @@ Close an issue or pull request.
 Reopen an issue or pull request.
 
 ```
-… then open;
+.open();
 ```
 
 #### `lock`
@@ -134,7 +106,7 @@ Reopen an issue or pull request.
 Lock conversation on an issue or pull request.
 
 ```
-… then lock;
+.lock();
 ```
 
 #### `unlock`
@@ -142,7 +114,7 @@ Lock conversation on an issue or pull request.
 Unlock conversation on an issue or pull request.
 
 ```
-… then unlock;
+.unlock();
 ```
 
 #### `label`
@@ -150,7 +122,7 @@ Unlock conversation on an issue or pull request.
 Add labels
 
 ```
-… then label(bug);
+.label('bug');
 ```
 
 #### `unlabel`
@@ -158,25 +130,25 @@ Add labels
 Add labels
 
 ```
-… then unlabel("needs-work") and label("waiting-for-review");
+.unlabel('needs-work').label('waiting-for-review');
 ```
 
 #### `assign`
 
 ```
-… then assign(hubot);
+.assign('hubot');
 ```
 
 #### `unassign`
 
 ```
-… then unassign(defunkt);
+.unassign('defunkt');
 ```
 
 #### `react`
 
 ```
-… then react(heart); # or +1, -1, laugh, confused, heart, hooray
+.react('heart'); # or +1, -1, laugh, confused, heart, hooray
 ```
 
 ---
diff --git a/docs/examples.md b/docs/examples.md
index 90498f2..9279a6f 100644
--- a/docs/examples.md
+++ b/docs/examples.md
@@ -6,75 +6,96 @@ Here are some examples of interesting things you can do by combining these compo
 
 ### Require use of issue template
 
-    # .github/MISSING_ISSUE_TEMPLATE_AUTOREPLY.md
-    #
-    # Hey @{{ sender.login }}, thanks for opening an issue. Unfortunately, you
-    # are missing information from the issue template. Please open a new issue with
-    # all the information from the template and it will make it easier for us to
-    # help you.
+```js
+// .github/MISSING_ISSUE_TEMPLATE_AUTOREPLY.md
+//
+// Hey @{{ sender.login }}, thanks for opening an issue. Unfortunately, you
+// are missing information from the issue template. Please open a new issue with
+// all the information from the template and it will make it easier for us to
+// help you.
 
-    on issues.opened
-    if
-      payload.body !matches /### Prerequisites.*### Description.*### Steps to Reproduce.*### Versions/
-      or payload.body matches /- [ ]/
-    then
-      comment(from_file(".github/MISSING_ISSUE_TEMPLATE_AUTOREPLY.md")
-      and label("insufficient-info")
-      and close;
+on('issues.opened')
+  .filter((event) => {
+      return !event.issue.body.match(/### Steps to Reproduce/)
+       || event.issue.body.includes('- [ ]')
+    })
+  .comment.contents('.github/MISSING_ISSUE_TEMPLATE_AUTOREPLY.md')
+  .label('insufficient-info')
+  .close();
+```
 
 ### Post welcome message for new contributors
 
-    on issues.opened or pull_request.opened
-    if first_time_contributor # plugins could implement conditions like this
-    then comment(file(".github/NEW_CONTRIBUTOR_TEMPLATE.md"));
+```js
+on('issues.opened', 'pull_request.opened')
+  .filter.firstTimeContributor() // plugins could implement conditions like this
+  .comment.contents('.github/NEW_CONTRIBUTOR_TEMPLATE.md');
+```
 
 ### Auto-close new pull requests
 
-    on pull_request.opened
-    then comment("Sorry @{{ user.login }}, pull requests are not accepted on this repository.")
-    and close;
+```js
+on('pull_request.opened')
+  .comment('Sorry @{{ user.login }}, pull requests are not accepted on this repository.')
+  .close();
+```
 
 ### Close issues with no body
 
-    on issues.opened
-    if @issue.body matches /^$/
-    then comment("Hey @{{ user.login }}, you didn't include a description of the problem, so we're closing this issue.");
+```js
+on('issues.opened')
+  .filter((event) => event.issue.body.match(/^$/))
+  .comment('Hey @{{ user.login }}, you didn't include a description of the problem, so we're closing this issue.');
+```
 
 ### @mention watchers when label added
 
-    on *.labeled then
-    # TODO: figure out syntax for loading watchers from file
-    comment("Hey {{ mentions }}, you wanted to know when the `{{ payload.label.name }}` label was added.");
+```js
+on('*.labeled')
+  // TODO: figure out syntax for loading watchers from file
+  .comment('Hey {{ mentions }}, you wanted to know when the `{{ payload.label.name }}` label was added.');
+```
 
 ### Assign a reviewer for new bugs
 
-    on pull_request.labeled
-    if labeled(bug)
-    then assign(random(file(OWNERS)));
+```js
+on('pull_request.labeled')
+  .filter((event) => event.labeled(bug))
+  .assign(random(file(OWNERS)));
+```
 
 ### Perform actions based on content of comments
 
-    on issue_comment.opened
-    if @issue.body matches /^@probot assign @(\w+)$/
-    then assign({{ matches[0] }})
+```js
+on('issue_comment.opened')
+  .filter((event) => event.issue.body.match(/^@probot assign @(\w+)$/))
+  .assign({{ matches[0] }});
 
-    on issue_comment.opened
-    if @issue.body matches /^@probot label @(\w+)$/
-    then label($1)
+on('issue_comment.opened')
+  .filter((event) => event.issue.body.match(/^@probot label @(\w+)$/))
+  .label($1);
+```
 
 ### Close stale issues and pull requests
 
-    on *.labeled
-    if labeled("needs-work") and state("open")
-    then delay(7 days) and close
+```js
+every('day')
+  .find.issues({state: 'open', label: 'needs-work'})
+  .filter.lastActive(7, 'days')
+  .close();
+```
 
 ### Tweet when a new release is created
 
-    on release.published
-    then tweet("Get it while it's hot! {{ repository.name }} {{ release.name }} was just released! {{ release.html_url }}")
+```js
+on('release.published')
+  .tweet("Get it while it's hot! {{ repository.name }} {{ release.name }} was just released! {{ release.html_url }}");
+```
 
 ### Assign a reviewer issues or pull requests with a label
 
-    on issues.opened and pull_request.opened and issues.labeled and pull_request.labeled
-    if labeled(security)
-    then assign(random(members(security-first-responders));
+```js
+on('issues.opened', 'pull_request.opened', 'issues.labeled', 'pull_request.labeled')
+  .filter.labeled('security')
+  .assign(team('security-first-responders').random());
+```
diff --git a/lib/actions.js b/lib/actions.js
deleted file mode 100644
index 6444c45..0000000
--- a/lib/actions.js
+++ /dev/null
@@ -1,13 +0,0 @@
-module.exports = {
-  assign: require('./actions/assign'),
-  close: require('./actions/close'),
-  comment: require('./actions/comment'),
-  label: require('./actions/label'),
-  lock: require('./actions/lock'),
-  open: require('./actions/open'),
-  unassign: require('./actions/unassign'),
-  unlabel: require('./actions/unlabel'),
-  unlock: require('./actions/unlock'),
-  react: require('./actions/react'),
-  updateIssue: require('./actions/update-issue')
-};
diff --git a/lib/actions/assign.js b/lib/actions/assign.js
deleted file mode 100644
index 527a642..0000000
--- a/lib/actions/assign.js
+++ /dev/null
@@ -1,16 +0,0 @@
-// Assign one or more users to an issue or pull request.
-//
-// ```
-// # Assign a single user
-// then assign(bkeepers);
-//
-// # Assign multiple users
-// then assign(bkeepers, benbalter);
-// ```
-//
-
-module.exports = function (context, ...logins) {
-  return context.github.issues.addAssigneesToIssue(
-    context.payload.toIssue({assignees: logins})
-  );
-};
diff --git a/lib/actions/close.js b/lib/actions/close.js
deleted file mode 100644
index 7f84f65..0000000
--- a/lib/actions/close.js
+++ /dev/null
@@ -1,5 +0,0 @@
-const updateIssue = require('./update-issue');
-
-module.exports = function (context) {
-  return updateIssue(context, {state: 'closed'});
-};
diff --git a/lib/actions/comment.js b/lib/actions/comment.js
deleted file mode 100644
index 67b4bf5..0000000
--- a/lib/actions/comment.js
+++ /dev/null
@@ -1,7 +0,0 @@
-const handlebars = require('handlebars');
-
-module.exports = function (context, template) {
-  return context.github.issues.createComment(
-    context.payload.toIssue({body: handlebars.compile(template)(context.payload)})
-  );
-};
diff --git a/lib/actions/label.js b/lib/actions/label.js
deleted file mode 100644
index 753ebdf..0000000
--- a/lib/actions/label.js
+++ /dev/null
@@ -1,5 +0,0 @@
-module.exports = function (context, ...labels) {
-  return context.github.issues.addLabels(
-    context.payload.toIssue({body: labels})
-  );
-};
diff --git a/lib/actions/lock.js b/lib/actions/lock.js
deleted file mode 100644
index 8a5cbab..0000000
--- a/lib/actions/lock.js
+++ /dev/null
@@ -1,3 +0,0 @@
-module.exports = function (context) {
-  return context.github.issues.lock(context.payload.toIssue());
-};
diff --git a/lib/actions/open.js b/lib/actions/open.js
deleted file mode 100644
index 27662cd..0000000
--- a/lib/actions/open.js
+++ /dev/null
@@ -1,5 +0,0 @@
-const updateIssue = require('./update-issue');
-
-module.exports = function (context) {
-  return updateIssue(context, {state: 'open'});
-};
diff --git a/lib/actions/react.js b/lib/actions/react.js
deleted file mode 100644
index 0fc27c5..0000000
--- a/lib/actions/react.js
+++ /dev/null
@@ -1,6 +0,0 @@
-
-module.exports = function (context, react) {
-  return context.github.reactions.createForIssue(
-    context.payload.toIssue({content: react})
-  );
-};
diff --git a/lib/actions/unassign.js b/lib/actions/unassign.js
deleted file mode 100644
index 936e02d..0000000
--- a/lib/actions/unassign.js
+++ /dev/null
@@ -1,16 +0,0 @@
-// Unassign one or more users from an issue or pull request.
-//
-// ```
-// # Unassign a single user
-// then unassign(bkeepers);
-//
-// # Unassign multiple users
-// then unassign(bkeepers, benbalter);
-// ```
-//
-
-module.exports = function (context, ...logins) {
-  return context.github.issues.removeAssigneesFromIssue(
-    context.payload.toIssue({body: {assignees: logins}})
-  );
-};
diff --git a/lib/actions/unlabel.js b/lib/actions/unlabel.js
deleted file mode 100644
index d4df621..0000000
--- a/lib/actions/unlabel.js
+++ /dev/null
@@ -1,9 +0,0 @@
-module.exports = (context, ...labels) => {
-  // FIXME: check that it has the label first, or handle expected error:
-  // {"message":"Label does not exist","documentation_url":"https://developer.github.com/v3/issues/labels/#remove-a-label-from-an-issue"}
-  return Promise.all(labels.map(label => {
-    return context.github.issues.removeLabel(
-      context.payload.toIssue({name: label})
-    );
-  }));
-};
diff --git a/lib/actions/unlock.js b/lib/actions/unlock.js
deleted file mode 100644
index 23fade2..0000000
--- a/lib/actions/unlock.js
+++ /dev/null
@@ -1,3 +0,0 @@
-module.exports = function (context) {
-  return context.github.issues.unlock(context.payload.toIssue());
-};
diff --git a/lib/actions/update-issue.js b/lib/actions/update-issue.js
deleted file mode 100644
index be003cf..0000000
--- a/lib/actions/update-issue.js
+++ /dev/null
@@ -1,4 +0,0 @@
-// https://mikedeboer.github.io/node-github/#api-issues-edit
-module.exports = function (context, attrs) {
-  return context.github.issues.edit(context.payload.toIssue(attrs));
-};
diff --git a/lib/attribute.js b/lib/attribute.js
deleted file mode 100644
index 5c52884..0000000
--- a/lib/attribute.js
+++ /dev/null
@@ -1,5 +0,0 @@
-module.exports = (context, name) => {
-  return name.reduce((object, attr) => {
-    return object ? object[attr] : null;
-  }, context.payload);
-};
diff --git a/lib/behavior.js b/lib/behavior.js
deleted file mode 100644
index 84f1666..0000000
--- a/lib/behavior.js
+++ /dev/null
@@ -1,17 +0,0 @@
-module.exports = class Behavior {
-  constructor(events, conditions, actions) {
-    this.events = events;
-    this.conditions = conditions;
-    this.actions = actions;
-  }
-
-  perform(context) {
-    if (this.conditions && !this.conditions(context)) {
-      return Promise.resolve();
-    }
-
-    return Promise.all(this.actions.map(action => {
-      return action(context);
-    }));
-  }
-};
diff --git a/lib/binary-expression.js b/lib/binary-expression.js
deleted file mode 100644
index e880120..0000000
--- a/lib/binary-expression.js
+++ /dev/null
@@ -1,24 +0,0 @@
-const operators = {
-  'is':               (left, right) => left === right,
-  'is not':           (left, right) => left !== right,
-  'contains':         (left, right) => left.includes(right),
-  'does not contain': (left, right) => !left.includes(right),
-  'matches':          (left, right) => left.match(right),
-  'does not match':   (left, right) => !left.match(right),
-  'or':               (left, right) => left || right,
-  'and':              (left, right) => left && right
-};
-
-function resolve(value, context) {
-  if (typeof value === 'function') {
-    return value(context);
-  } else {
-    return value;
-  }
-}
-
-module.exports = (context, left, operator, right) => {
-  const leftValue = resolve(left, context);
-  const rightValue = resolve(right, context);
-  return operators[operator](leftValue, rightValue);
-};
diff --git a/lib/conditions.js b/lib/conditions.js
deleted file mode 100644
index 70e5a21..0000000
--- a/lib/conditions.js
+++ /dev/null
@@ -1,3 +0,0 @@
-module.exports = {
-  labeled: require('./conditions/labeled')
-};
diff --git a/lib/conditions/labeled.js b/lib/conditions/labeled.js
deleted file mode 100644
index 618b031..0000000
--- a/lib/conditions/labeled.js
+++ /dev/null
@@ -1,3 +0,0 @@
-module.exports = (context, label) => {
-  return context.payload.label && context.payload.label.name === label;
-};
diff --git a/lib/configuration.js b/lib/configuration.js
index cbb3f3f..aecd74c 100644
--- a/lib/configuration.js
+++ b/lib/configuration.js
@@ -1,16 +1,16 @@
+const vm = require('vm');
 const debug = require('debug')('PRobot');
-const Transformer = require('./transformer');
-const parser = require('./parser');
+const Sandbox = require('./sandbox');
 
 module.exports = class Configuration {
   // Get bot config from target repository
   static load(github, repository) {
-    debug('Fetching .probot from %s', repository.full_name);
+    debug('Fetching .probot.js from %s', repository.full_name);
     const parts = repository.full_name.split('/');
     return github.repos.getContent({
       owner: parts[0],
       repo: parts[1],
-      path: '.probot'
+      path: '.probot.js'
     }).then(data => {
       const content = new Buffer(data.content, 'base64').toString();
       debug('Configuration fetched', content);
@@ -19,21 +19,19 @@ module.exports = class Configuration {
   }
 
   static parse(content) {
-    const transformer = new Transformer(parser.parse(content));
-    return new Configuration(transformer.transform());
+    const sandbox = new Sandbox();
+    vm.createContext(sandbox.api);
+    vm.runInContext(content, sandbox.api);
+    return new Configuration(sandbox.workflows);
   }
 
-  constructor(behaviors) {
-    this.behaviors = behaviors;
+  constructor(workflows) {
+    this.workflows = workflows;
   }
 
-  // FIXME: this can be moved into Behavior as a condition
-  behaviorsFor(event) {
-    return this.behaviors.filter(behavior => {
-      return behavior.events.filter(e => {
-        return e.name === event.event &&
-          (!e.action || e.action === event.payload.action);
-      }).length > 0;
+  workflowsFor(event) {
+    return this.workflows.filter(w => {
+      return w.matchesEvent(event) && w.filterFn(event);
     });
   }
 };
diff --git a/lib/dispatcher.js b/lib/dispatcher.js
index 63d9755..dc87d64 100644
--- a/lib/dispatcher.js
+++ b/lib/dispatcher.js
@@ -1,4 +1,5 @@
 const Context = require('./context');
+const issues = require('./plugins/issues');
 
 class Dispatcher {
   constructor(github, event) {
@@ -8,13 +9,23 @@ class Dispatcher {
 
   call(config) {
     // Get behaviors for the event
-    const behaviors = config.behaviorsFor(this.event);
     const context = new Context(this.github, config, this.event);
+    const workflows = config.workflowsFor(this.event);
+
+    // FIXME: have a better method to register evaluators
+    const evaluators = [
+      issues.Evaluator
+    ];
 
     // Handle all behaviors
-    return Promise.all(behaviors.map(behavior => {
-      return behavior.perform(context);
-    }));
+    return Promise.all(workflows.map(w => {
+      return evaluators.map(E => {
+        const evaluator = new E();
+        return evaluator.evaluate(w, context);
+      });
+    }).reduce((a, b) => {
+      return a.concat(b);
+    }, []));
   }
 }
 
diff --git a/lib/evaluator.js b/lib/evaluator.js
new file mode 100644
index 0000000..b3c1023
--- /dev/null
+++ b/lib/evaluator.js
@@ -0,0 +1,4 @@
+class Evaluator {
+}
+
+module.exports = Evaluator;
diff --git a/lib/parser.js b/lib/parser.js
deleted file mode 100644
index 295ec69..0000000
--- a/lib/parser.js
+++ /dev/null
@@ -1,21 +0,0 @@
-const fs = require('fs');
-const path = require('path');
-const PEG = require('pegjs');
-const PEGUtil = require('pegjs-util');
-
-// FIXME: eventually this should be generated on release
-const parser = PEG.generate(fs.readFileSync(path.join(__dirname, 'parser.pegjs'), 'utf8'), {
-  allowedStartRules: ['start', 'if']
-});
-
-module.exports = {
-  parse: (content, options) => {
-    const result = PEGUtil.parse(parser, content, options);
-
-    if (result.error) {
-      throw new Error('\n' + PEGUtil.errorMessage(result.error, true), null, result.error.line);
-    } else {
-      return result.ast;
-    }
-  }
-};
diff --git a/lib/parser.pegjs b/lib/parser.pegjs
deleted file mode 100644
index 60d8a89..0000000
--- a/lib/parser.pegjs
+++ /dev/null
@@ -1,160 +0,0 @@
-{
-  var unroll = options.util.makeUnroll(location, options)
-
-  // Helper Functions
-
-  function binaryExpression(head, tail) {
-    return tail.reduce(function(result, element) {
-      return {
-        type: 'BinaryExpression',
-        operator: element[1],
-        left: result,
-        right: element[3]
-      };
-    }, head);
-  }
-}
-
-start = _* b:behavior* _* { return b; }
-
-behavior
-  = _* events:on _ conditions:if _ actions:then _* semicolon {
-    return {
-      type: 'behavior',
-      events: events,
-      conditions: conditions,
-      actions: actions
-    };
-  }
-  / _* events:on _ actions:then _* semicolon {
-    return {
-      type: 'behavior',
-      events: events,
-      actions: actions
-    };
-  }
-
-// on
-
-on = "on" _ head:event tail:(_ or _ event)* { return unroll(head, tail, 3); }
-
-event
-  = e:word dot a:word { return {type: 'event', name: e, action: a}; }
-  / e:word { return {type: 'event', name: e}; }
-
-// if
-
-if = "if" _ conditions:RelationalExpression { return conditions; }
-
-RelationalExpression
-  = head:LogicalOrExpression tail:(_ RelationalOperator _ LogicalOrExpression)* {
-    return binaryExpression(head, tail);
-  }
-RelationalOperator
-  = "is not"
-  / "is"
-  / "does not contain"
-  / "contains"
-  / "does not match"
-  / "matches"
-
-LogicalOrExpression
-  = head:LogicalAndExpression tail:(_ or _ LogicalAndExpression)* {
-    return binaryExpression(head, tail);
-  }
-
-LogicalAndExpression
-  = head:UnaryExpression tail:(_ and _ UnaryExpression)* {
-    return binaryExpression(head, tail);
-  }
-
-UnaryExpression
-  = operand
-  / operator:UnaryOperator _ argument:UnaryExpression {
-    return {
-      type: 'UnaryExpression',
-      operator: operator,
-      argument: argument
-    }
-  }
-
-UnaryOperator = "not"
-
-operand = condition / attribute / string / boolean
-
-condition
-  = name:word "(" args:arguments ")" {
-    return {type: 'condition', name: name, args: args};
-  }
-
-attribute = "@" head:word tail:(dot word)* {
-  return {type: 'attribute', name: unroll(head, tail, 1)};
-}
-
-// then
-
-then
-  = "then" _ head:action tail:(_ and _ action)* {
-    return unroll(head, tail, 3);
-  }
-
-action
-  = name:word "(" _* args:arguments _* ")" {
-    return {type: 'action', name: name, args: args};
-  }
-  / name:word { return {type: 'action', name: name}; }
-
-arguments
-  = head:argument tail:(_* comma _* argument)* { return unroll(head, tail, 3); }
-
-argument = word / string
-
-boolean = true / false
-true = "true" { return true; }
-false = "false" { return false; }
-
-// Strings
-
-string "string"
-  = quotation_mark chars:char* quotation_mark { return chars.join(""); }
-
-char
-  = unescaped
-  / escape
-    sequence:(
-        '"'
-      / "\\"
-      / "/"
-      / "b" { return "\b"; }
-      / "f" { return "\f"; }
-      / "n" { return "\n"; }
-      / "r" { return "\r"; }
-      / "t" { return "\t"; }
-      / "u" digits:$(HEXDIG HEXDIG HEXDIG HEXDIG) {
-          return String.fromCharCode(parseInt(digits, 16));
-        }
-    )
-    { return sequence; }
-
-escape
-  = "\\"
-
-quotation_mark
-  = '"'
-
-unescaped
-  = [^\0-\x1F\x22\x5C]
-
-HEXDIG = [0-9a-f]i
-
-// Character Classes
-
-word = letters:[a-zA-Z0-9_]+ { return letters.join(''); }
-dot = "."
-comma = ","
-semicolon = ";"
-and = "and"
-or = "or"
-_ "whitespace" = ([ \t\n\r] / comment)+
-comment = "#" (!LineTerminator .)*
-LineTerminator = [\n\r\u2028\u2029]
diff --git a/lib/plugins/issues.js b/lib/plugins/issues.js
new file mode 100644
index 0000000..8f88793
--- /dev/null
+++ b/lib/plugins/issues.js
@@ -0,0 +1,160 @@
+const handlebars = require('handlebars');
+const Evaluator = require('../evaluator');
+
+const IssuePlugin = superclass => class extends superclass {
+  comment(content) {
+    this._setCommentData({content});
+    return this;
+  }
+
+  assign(...assignees) {
+    this._setCommentData({assignees});
+    return this;
+  }
+
+  unassign(...assignees) {
+    this._setCommentData({unassignees: assignees});
+    return this;
+  }
+
+  label(...labels) {
+    this._setCommentData({labels});
+    return this;
+  }
+
+  unlabel(...labels) {
+    this._setCommentData({unlabels: labels});
+    return this;
+  }
+
+  lock() {
+    this._setCommentData({lock: true});
+    return this;
+  }
+
+  unlock() {
+    this._setCommentData({unlock: true});
+    return this;
+  }
+
+  open() {
+    this._setCommentData({open: true});
+    return this;
+  }
+
+  close() {
+    this._setCommentData({close: true});
+    return this;
+  }
+
+  react(reaction) {
+    this._setCommentData({reaction});
+    return this;
+  }
+
+  _setCommentData(obj) {
+    if (this.issueActions === undefined) {
+      this.issueActions = {};
+    }
+    Object.assign(this.issueActions, obj);
+  }
+};
+
+// This is the function that implements all of the actions configured above.
+class IssueEvaluator extends Evaluator {
+  evaluate(workflow, context) {
+    const event = context.event;
+
+    // Bail if no issue related actions
+    if (workflow.issueActions === undefined) {
+      return;
+    }
+
+    // Need to guard to make sure we are only processing events we know what to
+    // do with. It might be nice to have it throw errors in a validation step
+    // so that people know when that they have actions that don't match their
+    // events.
+    if (event.issue !== undefined && event.pull_request !== undefined) {
+      return;
+    }
+    const promises = [];
+
+    if (workflow.issueActions.content !== undefined) {
+      const template = handlebars.compile(workflow.issueActions.content)(context.payload);
+
+      promises.push(
+        context.github.issues.createComment(context.payload.toIssue({body: template}))
+      );
+    }
+
+    if (workflow.issueActions.assignees !== undefined) {
+      const assignees = workflow.issueActions.assignees;
+      promises.push(
+        context.github.issues.addAssigneesToIssue(context.payload.toIssue({assignees}))
+      );
+    }
+
+    if (workflow.issueActions.unassignees !== undefined) {
+      const assignees = {assignees: workflow.issueActions.unassignees};
+      promises.push(
+        context.github.issues.removeAssigneesFromIssue(context.payload.toIssue({body: assignees}))
+      );
+    }
+
+    if (workflow.issueActions.labels !== undefined) {
+      const labels = workflow.issueActions.labels;
+      promises.push(
+        context.github.issues.addLabels(context.payload.toIssue({body: labels}))
+      );
+    }
+
+    if (workflow.issueActions.unlabels !== undefined) {
+      const labels = workflow.issueActions.unlabels;
+      promises.push(
+        labels.map(label => {
+          return context.github.issues.removeLabel(
+            context.payload.toIssue({name: label})
+          );
+        })
+      );
+    }
+
+    if (workflow.issueActions.lock !== undefined) {
+      promises.push(
+        context.github.issues.lock(context.payload.toIssue({}))
+      );
+    }
+
+    if (workflow.issueActions.unlock !== undefined) {
+      promises.push(
+        context.github.issues.unlock(context.payload.toIssue({}))
+      );
+    }
+
+    if (workflow.issueActions.open !== undefined) {
+      promises.push(
+        context.github.issues.edit(context.payload.toIssue({state: 'open'}))
+      );
+    }
+
+    if (workflow.issueActions.close !== undefined) {
+      promises.push(
+        context.github.issues.edit(context.payload.toIssue({state: 'closed'}))
+      );
+    }
+
+    if (workflow.issueActions.reaction !== undefined) {
+      const reaction = workflow.issueActions.reaction;
+      promises.push(
+        context.github.reactions.createForIssue(context.payload.toIssue({content: reaction}))
+      );
+    }
+
+    return promises;
+  }
+}
+
+module.exports = {
+  Plugin: IssuePlugin,
+  Evaluator: IssueEvaluator
+};
diff --git a/lib/sandbox.js b/lib/sandbox.js
new file mode 100644
index 0000000..632b282
--- /dev/null
+++ b/lib/sandbox.js
@@ -0,0 +1,19 @@
+const Workflow = require('./workflow');
+
+class Sandbox {
+  constructor() {
+    this.workflows = [];
+
+    this.api = {
+      on: this.on.bind(this)
+    };
+  }
+
+  on(...events) {
+    const workflow = new Workflow(events);
+    this.workflows.push(workflow);
+    return workflow;
+  }
+}
+
+module.exports = Sandbox;
diff --git a/lib/transformer.js b/lib/transformer.js
deleted file mode 100644
index 287e220..0000000
--- a/lib/transformer.js
+++ /dev/null
@@ -1,71 +0,0 @@
-const walk = require('tree-walk');
-const debug = require('debug')('PRobot');
-const Behavior = require('./behavior');
-const actions = require('./actions');
-const conditions = require('./conditions');
-const binaryExpression = require('./binary-expression');
-const attribute = require('./attribute');
-
-module.exports = class Transformer {
-  constructor(tree) {
-    this.tree = tree;
-  }
-
-  transform() {
-    return walk.reduce(this.tree, this.walk.bind(this));
-  }
-
-  walk(result, node) {
-    if (this[node.type]) {
-      return this[node.type](result, node);
-    } else if (node.type) {
-      throw new Error('Unknown node: ' + node.type);
-    } else {
-      return result || node;
-    }
-  }
-
-  event(node) {
-    return node;
-  }
-
-  attribute(node) {
-    return context => attribute(context, node.name);
-  }
-
-  action(node) {
-    return context => {
-      if (!actions[node.name]) {
-        throw new Error('Unknown action: ' + node.name);
-      }
-      debug('action: %s', node.name, node.args);
-      return actions[node.name].apply(context, [context].concat(node.args));
-    };
-  }
-
-  behavior(node) {
-    return new Behavior(node.events, node.conditions, node.actions);
-  }
-
-  condition(node) {
-    return context => {
-      if (!conditions[node.name]) {
-        throw new Error('Unknown condition: ' + node.name);
-      }
-      debug('condition: %s', node.name, node.args);
-      return conditions[node.name].apply(context, [context].concat(node.args));
-    };
-  }
-
-  BinaryExpression(node) {
-    return context => {
-      return binaryExpression(context, node.left, node.operator, node.right);
-    };
-  }
-
-  UnaryExpression(node) {
-    return context => {
-      return !node.argument(context);
-    };
-  }
-};
diff --git a/lib/workflow.js b/lib/workflow.js
new file mode 100644
index 0000000..70ee131
--- /dev/null
+++ b/lib/workflow.js
@@ -0,0 +1,41 @@
+const issues = require('./plugins/issues');
+
+class WorkflowCore {
+  constructor(events) {
+    this.events = events;
+    this.filterFn = () => true;
+  }
+
+  filter(fn) {
+    this.filterFn = fn;
+    return this;
+  }
+
+  matchesEvent(event) {
+    const eventWithAction = [event.event, event.payload.action];
+
+    return this.events.find(e => {
+      const parts = e.split('.');
+      for (let i = 0; i < parts.length; i++) {
+        if (parts[i] !== eventWithAction[i]) {
+          return false;
+        }
+      }
+      return true;
+    });
+  }
+}
+
+// FIXME: issues
+const plugins = [
+  issues.Plugin
+];
+
+// Helper to combine an array of mixins into one class
+function mix(superclass, ...mixins) {
+  return mixins.reduce((c, mixin) => mixin(c), superclass);
+}
+
+class Workflow extends mix(WorkflowCore, ...plugins) {}
+
+module.exports = Workflow;
diff --git a/package.json b/package.json
index 298a9cb..d9739d1 100644
--- a/package.json
+++ b/package.json
@@ -14,11 +14,7 @@
     "expect": "^1.20.2",
     "github": "^5.2.0",
     "github-webhook-handler": "^0.6.0",
-    "handlebars": "^4.0.5",
-    "jsdoc": "^3.4.2",
-    "pegjs": "^0.10.0",
-    "pegjs-util": "^1.4.0",
-    "tree-walk": "^0.4.0"
+    "handlebars": "^4.0.5"
   },
   "devDependencies": {
     "mocha": "^3.0.2",
diff --git a/test/actions/assign.js b/test/actions/assign.js
deleted file mode 100644
index 6ce75f1..0000000
--- a/test/actions/assign.js
+++ /dev/null
@@ -1,36 +0,0 @@
-const expect = require('expect');
-const action = require('../../lib/actions/assign');
-const Context = require('../../lib/context');
-const payload = require('../fixtures/webhook/comment.created.json');
-
-const createSpy = expect.createSpy;
-
-const github = {
-  issues: {
-    addAssigneesToIssue: createSpy()
-  }
-};
-
-const context = new Context(github, {}, {payload});
-
-describe('action.assign', () => {
-  it('assigns a user', () => {
-    action(context, 'bkeepers');
-    expect(github.issues.addAssigneesToIssue).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      assignees: ['bkeepers']
-    });
-  });
-
-  it('assigns multiple users', () => {
-    action(context, 'hello', 'world');
-    expect(github.issues.addAssigneesToIssue).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      assignees: ['hello', 'world']
-    });
-  });
-});
diff --git a/test/actions/comment.js b/test/actions/comment.js
deleted file mode 100644
index d42d1ae..0000000
--- a/test/actions/comment.js
+++ /dev/null
@@ -1,25 +0,0 @@
-const expect = require('expect');
-const action = require('../../lib/actions/comment');
-const Context = require('../../lib/context');
-const payload = require('../fixtures/webhook/comment.created.json');
-
-const createSpy = expect.createSpy;
-
-const github = {
-  issues: {
-    createComment: createSpy()
-  }
-};
-
-describe('action.comment', () => {
-  it('creates a comment', () => {
-    const context = new Context(github, {}, {payload});
-    action(context, 'Hello @{{ sender.login }}!');
-    expect(github.issues.createComment).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      body: 'Hello @bkeepers!'
-    });
-  });
-});
diff --git a/test/actions/label.js b/test/actions/label.js
deleted file mode 100644
index 39bc472..0000000
--- a/test/actions/label.js
+++ /dev/null
@@ -1,35 +0,0 @@
-const expect = require('expect');
-const action = require('../../lib/actions/label');
-const Context = require('../../lib/context');
-const payload = require('../fixtures/webhook/comment.created.json');
-
-const createSpy = expect.createSpy;
-
-const github = {
-  issues: {
-    addLabels: createSpy()
-  }
-};
-const context = new Context(github, {}, {payload});
-
-describe('action.label', () => {
-  it('adds a label', () => {
-    action(context, 'hello');
-    expect(github.issues.addLabels).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      body: ['hello']
-    });
-  });
-
-  it('adds multiple labels', () => {
-    action(context, ['hello', 'world']);
-    expect(github.issues.addLabels).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      body: ['hello']
-    });
-  });
-});
diff --git a/test/actions/unassign.js b/test/actions/unassign.js
deleted file mode 100644
index f4f351b..0000000
--- a/test/actions/unassign.js
+++ /dev/null
@@ -1,35 +0,0 @@
-const expect = require('expect');
-const action = require('../../lib/actions/unassign');
-const Context = require('../../lib/context');
-const payload = require('../fixtures/webhook/comment.created.json');
-
-const createSpy = expect.createSpy;
-
-const github = {
-  issues: {
-    removeAssigneesFromIssue: createSpy()
-  }
-};
-const context = new Context(github, {}, {payload});
-
-describe('action.unassign', () => {
-  it('unassigns a user', () => {
-    action(context, 'bkeepers');
-    expect(github.issues.removeAssigneesFromIssue).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      body: {assignees: ['bkeepers']}
-    });
-  });
-
-  it('unassigns multiple users', () => {
-    action(context, 'hello', 'world');
-    expect(github.issues.removeAssigneesFromIssue).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      body: {assignees: ['hello', 'world']}
-    });
-  });
-});
diff --git a/test/actions/unlabel.js b/test/actions/unlabel.js
deleted file mode 100644
index 4d21409..0000000
--- a/test/actions/unlabel.js
+++ /dev/null
@@ -1,42 +0,0 @@
-const expect = require('expect');
-const action = require('../../lib/actions/unlabel');
-const Context = require('../../lib/context');
-const payload = require('../fixtures/webhook/comment.created.json');
-
-const createSpy = expect.createSpy;
-
-const github = {
-  issues: {
-    removeLabel: createSpy()
-  }
-};
-const context = new Context(github, {}, {payload});
-
-describe('action.unlabel', () => {
-  it('removes a single label', () => {
-    action(context, 'hello');
-    expect(github.issues.removeLabel).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      name: 'hello'
-    });
-  });
-
-  it('removes a multiple labels', () => {
-    action(context, 'hello', 'goodbye');
-    expect(github.issues.removeLabel).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      name: 'hello'
-    });
-
-    expect(github.issues.removeLabel).toHaveBeenCalledWith({
-      owner: 'bkeepers-inc',
-      repo: 'test',
-      number: 6,
-      name: 'goodbye'
-    });
-  });
-});
diff --git a/test/attribute.js b/test/attribute.js
deleted file mode 100644
index 4e741ac..0000000
--- a/test/attribute.js
+++ /dev/null
@@ -1,16 +0,0 @@
-const expect = require('expect');
-const attribute = require('../lib/attribute');
-
-describe('attribute', () => {
-  it('fetches the attribute from the payload', () => {
-    const context = {payload: {foo: {bar: 'baz'}}};
-    const value = attribute(context, ['foo', 'bar']);
-    expect(value).toEqual('baz');
-  });
-
-  it('returns null for unknown attributes', () => {
-    const context = {payload: {}};
-    const value = attribute(context, ['foo', 'unknown']);
-    expect(value).toEqual(null);
-  });
-});
diff --git a/test/conditions.js b/test/conditions.js
deleted file mode 100644
index b985fd8..0000000
--- a/test/conditions.js
+++ /dev/null
@@ -1,105 +0,0 @@
-const expect = require('expect');
-const Transformer = require('../lib/transformer');
-const Context = require('../lib/context');
-const parser = require('../lib/parser');
-const payload = require('./fixtures/webhook/issues.labeled.json');
-
-const context = new Context({}, {}, {payload});
-
-function test(string) {
-  const ast = parser.parse(string, {startRule: 'if'});
-  const condition = new Transformer(ast).transform();
-  return typeof condition === 'function' ? condition(context) : condition;
-}
-
-describe('conditions', () => {
-  describe('is', () => {
-    it('passes when operands are equal', () => {
-      expect(test(`if @sender.login is "bkeepers"`)).toBeTruthy();
-    });
-
-    it('fails when operands are not equal', () => {
-      expect(test(`if @sender.login is "nobody"`)).toBeFalsy();
-    });
-  });
-
-  describe('is not', () => {
-    it('fails when operands are equal', () => {
-      expect(test('if @sender.login is not "bkeepers"')).toBeFalsy();
-    });
-
-    it('passes when operands are not equal', () => {
-      expect(test('if @sender.login is not "nobody"')).toBeTruthy();
-    });
-  });
-
-  describe('contains', () => {
-    it('passes when operand contains substring', () => {
-      expect(test('if @issue.title contains "bug"')).toBeTruthy();
-    });
-
-    it('fails when operand does not contain substring', () => {
-      expect(test('if @issue.title contains "nope"')).toBeFalsy();
-    });
-  });
-
-  describe('does not contain', () => {
-    it('fails when operand contains substring', () => {
-      expect(test('if @issue.title does not contain "bug"')).toBeFalsy();
-    });
-
-    it('passes when operand does not contain substring', () => {
-      expect(test('if @issue.title does not contain "nope"')).toBeTruthy();
-    });
-  });
-
-  describe('matches', () => {
-    it('passes when operand matches regexp', () => {
-      expect(test('if @sender.login matches "ke+"')).toBeTruthy();
-    });
-
-    it('fails when operand does not match regexp', () => {
-      expect(test('if @issue.title matches "nope"')).toBeFalsy();
-    });
-  });
-
-  describe('does not match', () => {
-    it('fails when operand matches regexp', () => {
-      expect(test('if @sender.login does not match "ke+"')).toBeFalsy();
-    });
-
-    it('passes when operand does not match regexp', () => {
-      expect(test('if @issue.title does not match "nope"')).toBeTruthy();
-    });
-  });
-
-  describe('or', () => {
-    it('passes if either operand is truthy', () => {
-      expect(test('if labeled(bug) or labeled(feature)')).toBeTruthy();
-    });
-
-    it('fails if neither operand is truthy', () => {
-      expect(test('if labeled(nope) or labeled(never)')).toBeFalsy();
-    });
-  });
-
-  describe('and', () => {
-    it('passes if both operands are truthy', () => {
-      expect(test('if labeled(bug) and @issue.title contains "bug"')).toBeTruthy();
-    });
-
-    it('fails if one operand is not truthy', () => {
-      expect(test('if labeled(bug) and labeled(nope)')).toBeFalsy();
-    });
-  });
-
-  describe('not', () => {
-    it('passes if condition is not truthy', () => {
-      expect(test('if not labeled(something)')).toBeTruthy();
-    });
-
-    it('fails if condition is truthy', () => {
-      expect(test('if not labeled(bug)')).toBeFalsy();
-    });
-  });
-});
diff --git a/test/configuration.js b/test/configuration.js
index 27f9f09..875cf14 100644
--- a/test/configuration.js
+++ b/test/configuration.js
@@ -4,6 +4,16 @@ const config = require('./fixtures/content/probot.json');
 
 const createSpy = expect.createSpy;
 
+config.content = new Buffer(`
+  on("issues.opened")
+    .comment("Hello World!")
+    .assign("bkeepers")
+    .react("heart");
+
+  on("issues.closed")
+    .unassign("bkeepers");
+`).toString('base64');
+
 describe('Configuration', () => {
   describe('load', () => {
     let github;
@@ -23,32 +33,32 @@ describe('Configuration', () => {
         expect(github.repos.getContent).toHaveBeenCalledWith({
           owner: 'bkeepers',
           repo: 'test',
-          path: '.probot'
+          path: '.probot.js'
         });
 
-        expect(config.behaviors.length).toEqual(2);
+        expect(config.workflows.length).toEqual(2);
 
         done();
       });
     });
   });
 
-  describe('behaviorsFor', () => {
+  describe('workflowsFor', () => {
     const config = Configuration.parse(`
-      on issues then label(active);
-      on issues.created then close;
-      on pull_request.labeled then lock;
+      on("issues").label("active");
+      on("issues.created").close();
+      on("pull_request.labeled").lock();
     `);
 
     it('returns behaviors for event', () => {
       expect(
-        config.behaviorsFor({event: 'issues', payload: {}}).length
+        config.workflowsFor({event: 'issues', payload: {}}).length
       ).toEqual(1);
     });
 
     it('returns behaviors for event and action', () => {
       expect(
-        config.behaviorsFor({event: 'issues', payload: {action: 'created'}}).length
+        config.workflowsFor({event: 'issues', payload: {action: 'created'}}).length
       ).toEqual(2);
     });
   });
diff --git a/test/dispatcher.js b/test/dispatcher.js
index 6f12e83..64f0860 100644
--- a/test/dispatcher.js
+++ b/test/dispatcher.js
@@ -22,7 +22,7 @@ describe('dispatch', () => {
 
   describe('reply to new issue with a comment', () => {
     it('posts a coment', () => {
-      const config = Configuration.parse('on issues then comment("Hello World!");');
+      const config = Configuration.parse('on("issues").comment("Hello World!")');
       return dispatcher.call(config).then(() => {
         expect(github.issues.createComment).toHaveBeenCalled();
       });
@@ -31,7 +31,7 @@ describe('dispatch', () => {
 
   describe('reply to new issue with a comment', () => {
     it('calls the action', () => {
-      const config = Configuration.parse('on issues.created then comment("Hello World!");');
+      const config = Configuration.parse('on("issues.created").comment("Hello World!")');
 
       return dispatcher.call(config).then(() => {
         expect(github.issues.createComment).toHaveBeenCalled();
@@ -41,7 +41,7 @@ describe('dispatch', () => {
 
   describe('on an event with a different action', () => {
     it('does not perform behavior', () => {
-      const config = Configuration.parse('on issues.labeled then comment("Hello World!");');
+      const config = Configuration.parse('on("issues.labeled").comment("Hello World!")');
 
       return dispatcher.call(config).then(() => {
         expect(github.issues.createComment).toNotHaveBeenCalled();
@@ -49,7 +49,7 @@ describe('dispatch', () => {
     });
   });
 
-  describe('conditions', () => {
+  describe('filter', () => {
     beforeEach(() => {
       const labeled = require('./fixtures/webhook/issues.labeled.json');
 
@@ -58,20 +58,15 @@ describe('dispatch', () => {
       dispatcher = new Dispatcher(github, event);
     });
 
-    it('fails for unknown conditions', () => {
-      const config = Configuration.parse(`on issues.labeled if failwhale(bug) then close;`);
-      expect(() => dispatcher.call(config)).toThrow(/unknown condition/i);
-    });
-
     it('calls action when condition matches', () => {
-      const config = Configuration.parse(`on issues.labeled if labeled(bug) then close;`);
+      const config = Configuration.parse('on("issues.labeled").filter((e) => e.payload.label.name == "bug").close()');
       return dispatcher.call(config).then(() => {
         expect(github.issues.edit).toHaveBeenCalled();
       });
     });
 
     it('does not call action when conditions do not match', () => {
-      const config = Configuration.parse(`on issues.labeled if labeled(foobar) then close;`);
+      const config = Configuration.parse('on("issues.labeled").filter((e) => e.payload.label.name == "foobar").close()');
       return dispatcher.call(config).then(() => {
         expect(github.issues.edit).toNotHaveBeenCalled();
       });
diff --git a/test/fixtures/behaviors b/test/fixtures/behaviors
deleted file mode 100644
index 5c4e976..0000000
--- a/test/fixtures/behaviors
+++ /dev/null
@@ -1,29 +0,0 @@
-# Integration test
-
-on issues # ignore this
-then close;
-
-on issues then assign(hubot, probot);
-
-on issues.assign
-if labeled(foo) and labeled(bar) or labeled(baz)
-then close and comment("nope!");
-
-on issues.opened
-if @issue.user.login matches "bot$"
-then comment("No bots allowed!") and close;
-
-on issues.opened if @sender.login is "bkeepers" then close;
-on issues.opened if @sender.login is not "bkeepers" then close;
-on issues.opened if @issue.body contains "- [ ]" then label(wip);
-
-on issues.opened
-if not labeled(bug)
-then close;
-
-on issues.opened
-if @issue.body does not match "### Prerequisites.*### Description.*### Steps to Reproduce.*### Versions"
-  or @issue.body.body contains "- [ ]"
-then
-  label("insufficient-info")
-  and close;
diff --git a/test/fixtures/content/probot.json b/test/fixtures/content/probot.json
index 79dcd3d..4aca345 100644
--- a/test/fixtures/content/probot.json
+++ b/test/fixtures/content/probot.json
@@ -1,6 +1,6 @@
 {
-  "name": ".probot",
-  "path": ".probot",
+  "name": ".probot.js",
+  "path": ".probot.js",
   "sha": "c0736435c3f35dc5702d5024ed00d399b99623af",
   "size": 127,
   "url": "https://api.github.com/repos/bkeepers-inc/test/contents/.probot?ref=master",
@@ -8,7 +8,7 @@
   "git_url": "https://api.github.com/repos/bkeepers-inc/test/git/blobs/c0736435c3f35dc5702d5024ed00d399b99623af",
   "download_url": "https://raw.githubusercontent.com/bkeepers-inc/test/master/.probot?token=AVvMVIL7kvcrgJYZEipG9eAgUPcGHBnxks5YBayLwA%3D%3D",
   "type": "file",
-  "content": "b24gaXNzdWVzLm9wZW5lZCB0aGVuIGNvbW1lbnQoIkhlbGxvIHdvcmxkISIp\nIGFuZCBhc3NpZ24oYmtlZXBlcnMpIGFuZCByZWFjdChoZWFydCk7Cm9uIGlz\nc3Vlcy5jbG9zZWQgdGhlbiB1bmFzc2lnbihia2VlcGVycyk7Cg==\n",
+  "content": "d29ya2Zsb3dzLnB1c2goCiAgb24oImlzc3Vlcy5vcGVuZWQiKQogICAgLmNv\nbW1lbnQoIkhlbGxvIFdvcmxkISIpCiAgICAuYXNzaWduKCJia2VlcGVycyIp\nCiAgICAucmVhY3QoImhlYXJ0IikKKQoKd29ya2Zsb3dzLnB1c2goCiAgb24o\nImlzc3Vlcy5jbG9zZWQiKQogICAgLnVuYXNzaWduKCJia2VlcGVycyIpCikK\n",
   "encoding": "base64",
   "_links": {
     "self": "https://api.github.com/repos/bkeepers-inc/test/contents/.probot?ref=master",
diff --git a/test/parser.js b/test/parser.js
deleted file mode 100644
index 14329b0..0000000
--- a/test/parser.js
+++ /dev/null
@@ -1,261 +0,0 @@
-const fs = require('fs');
-const expect = require('expect');
-const parser = require('../lib/parser');
-
-describe('parser', () => {
-  it('successfully parses a bunch of examples', () => {
-    parser.parse(fs.readFileSync('./test/fixtures/behaviors').toString());
-  });
-
-  it('reports syntax errors', () => {
-    expect(() => parser.parse('lolwut?').toThrow(/parse error/));
-  });
-
-  it('parses multiple statements', () => {
-    expect(parser.parse(`
-      on issues.opened then close;
-      on pull_requests.open then assign(bkeepers);
-    `)).toEqual([
-      {
-        type: 'behavior',
-        events: [{type: 'event', action: 'opened', name: 'issues'}],
-        actions: [{type: 'action', name: 'close'}]
-      },
-      {
-        type: 'behavior',
-        events: [{type: 'event', action: 'open', name: 'pull_requests'}],
-        actions: [{type: 'action', name: 'assign', args: ['bkeepers']}]
-      }
-    ]);
-  });
-
-  it('parses a blank doc', () => {
-    expect(parser.parse('\n\n\n')).toEqual([]);
-  });
-
-  it('fails on junk', () => {
-    expect(() => parser.parse('onnope then nope;')).toThrow();
-    expect(() => parser.parse('on nope thennope;')).toThrow();
-  });
-
-  describe('on', () => {
-    it('parses an event', () => {
-      expect(parser.parse('on issues then close;')).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        actions: [{type: 'action', name: 'close'}]
-      }]);
-    });
-
-    it('parses an event and action', () => {
-      expect(parser.parse('on issues.opened then close;')).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues', action: 'opened'}],
-        actions: [{type: 'action', name: 'close'}]
-      }]);
-    });
-
-    it('parses multiple events', () => {
-      expect(parser.parse(
-        'on issues.opened or pull_request.opened then close;'
-      )).toEqual([{
-        type: 'behavior',
-        events: [
-          {type: 'event', name: 'issues', action: 'opened'},
-          {type: 'event', name: 'pull_request', action: 'opened'}
-        ],
-        actions: [{type: 'action', name: 'close'}]
-      }]);
-    });
-  });
-
-  describe('if', () => {
-    function parse(string) {
-      return parser.parse(string, {startRule: 'if'});
-    }
-
-    it('parses simple conditionals', () => {
-      expect(
-        parser.parse('on issues if labeled(enhancement) then close;')
-      ).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        conditions: {type: 'condition', name: 'labeled', args: ['enhancement']},
-        actions: [{type: 'action', name: 'close'}]
-      }]);
-    });
-
-    it('parses logical or conditions', () => {
-      expect(parse('if labeled(enhancement) or labeled(design)')).toEqual({
-        type: 'BinaryExpression',
-        operator: 'or',
-        left: {type: 'condition', name: 'labeled', args: ['enhancement']},
-        right: {type: 'condition', name: 'labeled', args: ['design']}
-      });
-    });
-
-    it('parses multiple logical conditions', () => {
-      expect(
-        parse('if labeled(enhancement) or labeled(design) or labeled(bug)')
-      ).toEqual({
-        type: 'BinaryExpression',
-        operator: 'or',
-        left: {
-          type: 'BinaryExpression',
-          left: {type: 'condition', name: 'labeled', args: ['enhancement']},
-          operator: 'or',
-          right: {type: 'condition', name: 'labeled', args: ['design']}
-        },
-        right: {type: 'condition', name: 'labeled', args: ['bug']}
-      });
-    });
-
-    it('parses logical and conditions', () => {
-      expect(parse('if labeled(enhancement) and labeled(design)')).toEqual({
-        type: 'BinaryExpression',
-        operator: 'and',
-        left: {type: 'condition', name: 'labeled', args: ['enhancement']},
-        right: {type: 'condition', name: 'labeled', args: ['design']}
-      });
-    });
-
-    it('parses attributes, matches, and regexps', () => {
-      expect(parse('if @issue.user.login matches "bot$"')).toEqual({
-        type: 'BinaryExpression',
-        operator: 'matches',
-        left: {type: 'attribute', name: ['issue', 'user', 'login']},
-        right: 'bot$'
-      });
-    });
-
-    describe('not', () => {
-      it('negates conditions', () => {
-        expect(parse('if not labeled(bug)')).toEqual({
-          type: 'UnaryExpression',
-          operator: 'not',
-          argument: {type: 'condition', name: 'labeled', args: ['bug']}
-        });
-      });
-    });
-
-    describe('precedence', () => {
-      it('orders "and" over "or"', () => {
-        expect(parse('if true and false or true')).toEqual({
-          type: 'BinaryExpression',
-          left: {
-            type: 'BinaryExpression',
-            left: true,
-            operator: 'and',
-            right: false
-          },
-          operator: 'or',
-          right: true
-        });
-
-        expect(parse('if false or true and true')).toEqual({
-          type: 'BinaryExpression',
-          left: false,
-          operator: 'or',
-          right: {
-            type: 'BinaryExpression',
-            left: true,
-            operator: 'and',
-            right: true
-          }
-        });
-
-        expect(parse('if true and true or false and false')).toEqual({
-          type: 'BinaryExpression',
-          left: {
-            type: 'BinaryExpression',
-            left: true,
-            operator: 'and',
-            right: true
-          },
-          operator: 'or',
-          right: {
-            type: 'BinaryExpression',
-            left: false,
-            operator: 'and',
-            right: false
-          }
-        });
-      });
-    });
-  });
-
-  describe('then', () => {
-    it('parses multiple words', () => {
-      expect(parser.parse(
-        'on issues then close and lock;'
-      )).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        actions: [
-          {type: 'action', name: 'close'},
-          {type: 'action', name: 'lock'}
-        ]
-      }]);
-    });
-
-    it('parses string arguments', () => {
-      expect(parser.parse(
-        'on issues then comment("Hello World!");'
-      )).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        actions: [
-          {type: 'action', name: 'comment', args: ['Hello World!']}
-        ]
-      }]);
-    });
-
-    it('parses word arguments', () => {
-      expect(parser.parse(
-        'on issues then assign(bkeepers);'
-      )).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        actions: [
-          {type: 'action', name: 'assign', args: ['bkeepers']}
-        ]
-      }]);
-    });
-
-    it('parses multiple word arguments', () => {
-      expect(parser.parse(
-        'on issues then assign(bkeepers, hubot);'
-      )).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        actions: [
-          {type: 'action', name: 'assign', args: ['bkeepers', 'hubot']}
-        ]
-      }]);
-    });
-  });
-
-  describe('comments', () => {
-    it('ignores lines that start with comments', () => {
-      expect(parser.parse(`
-        # This could literally be anything.
-        on issues then close;
-      `)).toEqual(
-        [{type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        actions: [{type: 'action', name: 'close'}]}]
-      );
-    });
-
-    it('ignores trailing comments on lines', () => {
-      expect(parser.parse(`
-        on issues # Ignore this
-        then close;
-      `)).toEqual([{
-        type: 'behavior',
-        events: [{type: 'event', name: 'issues'}],
-        actions: [{type: 'action', name: 'close'}]
-      }]);
-    });
-  });
-});
diff --git a/test/plugins/issues.js b/test/plugins/issues.js
new file mode 100644
index 0000000..0637d96
--- /dev/null
+++ b/test/plugins/issues.js
@@ -0,0 +1,227 @@
+const expect = require('expect');
+const issues = require('../../lib/plugins/issues');
+const Workflow = require('../../lib/workflow');
+const Context = require('../../lib/context');
+const payload = require('../fixtures/webhook/comment.created.json');
+
+const createSpy = expect.createSpy;
+
+const github = {
+  reactions: {
+    createForIssue: createSpy()
+  },
+  issues: {
+    lock: createSpy(),
+    unlock: createSpy(),
+    edit: createSpy(),
+    addLabels: createSpy(),
+    createComment: createSpy(),
+    addAssigneesToIssue: createSpy(),
+    removeAssigneesFromIssue: createSpy(),
+    removeLabel: createSpy()
+  }
+};
+const context = new Context(github, {}, {payload});
+
+describe('issues plugin', () => {
+  before(() => {
+    this.w = new Workflow();
+    this.evaluator = new issues.Evaluator();
+  });
+
+  describe('locking', () => {
+    it('locks', () => {
+      this.w.lock();
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.lock).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6
+      });
+    });
+
+    it('unlocks', () => {
+      this.w.unlock();
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.unlock).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6
+      });
+    });
+  });
+
+  describe('state', () => {
+    it('opens an issue', () => {
+      this.w.open();
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.edit).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        state: 'open'
+      });
+    });
+    it('closes an issue', () => {
+      this.w.close();
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.edit).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        state: 'closed'
+      });
+    });
+  });
+
+  describe('labels', () => {
+    it('adds a label', () => {
+      this.w.label('hello');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.addLabels).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        body: ['hello']
+      });
+    });
+
+    it('adds multiple labels', () => {
+      this.w.label('hello', 'world');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.addLabels).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        body: ['hello', 'world']
+      });
+    });
+
+    it('removes a single label', () => {
+      this.w.unlabel('hello');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.removeLabel).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        name: 'hello'
+      });
+    });
+
+    it('removes a multiple labels', () => {
+      this.w.unlabel('hello', 'goodbye');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.removeLabel).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        name: 'hello'
+      });
+
+      expect(github.issues.removeLabel).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        name: 'goodbye'
+      });
+    });
+  });
+
+  describe('comments', () => {
+    it('creates a comment', () => {
+      this.w.comment('Hello world!');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.createComment).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        body: 'Hello world!'
+      });
+    });
+
+    it('evaluates templates with handlebars', () => {
+      this.w.comment('Hello @{{ sender.login }}!');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.createComment).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        body: 'Hello @bkeepers!'
+      });
+    });
+  });
+
+  describe('assignment', () => {
+    it('assigns a user', () => {
+      this.w.assign('bkeepers');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.addAssigneesToIssue).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        assignees: ['bkeepers']
+      });
+    });
+
+    it('assigns multiple users', () => {
+      this.w.assign('hello', 'world');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.addAssigneesToIssue).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        assignees: ['hello', 'world']
+      });
+    });
+
+    it('unassigns a user', () => {
+      this.w.unassign('bkeepers');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.removeAssigneesFromIssue).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        body: {assignees: ['bkeepers']}
+      });
+    });
+
+    it('unassigns multiple users', () => {
+      this.w.unassign('hello', 'world');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.issues.removeAssigneesFromIssue).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        body: {assignees: ['hello', 'world']}
+      });
+    });
+  });
+
+  describe('reactions', () => {
+    it('react', () => {
+      this.w.react('heart');
+
+      Promise.all(this.evaluator.evaluate(this.w, context));
+      expect(github.reactions.createForIssue).toHaveBeenCalledWith({
+        owner: 'bkeepers-inc',
+        repo: 'test',
+        number: 6,
+        content: 'heart'
+      });
+    });
+  });
+});