diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..b04a8c8
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,11 @@
+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
+
+# rspec failure tracking
+.rspec_status
diff --git a/.rspec b/.rspec
new file mode 100644
index 0000000..34c5164
--- /dev/null
+++ b/.rspec
@@ -0,0 +1,3 @@
+--format documentation
+--color
+--require spec_helper
diff --git a/.ruby-version b/.ruby-version
new file mode 100644
index 0000000..61013db
--- /dev/null
+++ b/.ruby-version
@@ -0,0 +1 @@
+2.6.0-preview3
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..0ff124d
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,7 @@
+---
+sudo: false
+language: ruby
+cache: bundler
+rvm:
+  - 2.6.0
+before_install: gem install bundler -v 1.17.1
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
new file mode 100644
index 0000000..4bd8b99
--- /dev/null
+++ b/CODE_OF_CONDUCT.md
@@ -0,0 +1,74 @@
+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, gender identity and expression, level of experience,
+nationality, personal appearance, race, religion, or sexual identity and
+orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+* Using welcoming and inclusive language
+* Being respectful of differing viewpoints and experiences
+* Gracefully accepting constructive criticism
+* Focusing on what is best for the community
+* Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery and unwelcome sexual attention or
+advances
+* Trolling, insulting/derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or electronic
+  address, without explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned to this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported by contacting the project team at oleg.b.antonyan@gmail.com. All
+complaints will be reviewed and investigated and will result in a response that
+is deemed necessary and appropriate to the circumstances. The project team is
+obligated to maintain confidentiality with regard to the reporter of an incident.
+Further details of specific enforcement policies may be posted separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by other
+members of the project's leadership.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4,
+available at [http://contributor-covenant.org/version/1/4][version]
+
+[homepage]: http://contributor-covenant.org
+[version]: http://contributor-covenant.org/version/1/4/
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..03b626b
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,6 @@
+source "https://rubygems.org"
+
+git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
+
+# Specify your gem's dependencies in typerb.gemspec
+gemspec
diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 0000000..5f4c20a
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,45 @@
+PATH
+  remote: .
+  specs:
+    typerb (0.1.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    awesome_print (1.8.0)
+    coderay (1.1.2)
+    diff-lcs (1.3)
+    method_source (0.9.1)
+    pry (0.12.0)
+      coderay (~> 1.1.0)
+      method_source (~> 0.9.0)
+    rake (10.5.0)
+    rspec (3.8.0)
+      rspec-core (~> 3.8.0)
+      rspec-expectations (~> 3.8.0)
+      rspec-mocks (~> 3.8.0)
+    rspec-core (3.8.0)
+      rspec-support (~> 3.8.0)
+    rspec-expectations (3.8.2)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.8.0)
+    rspec-mocks (3.8.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.8.0)
+    rspec-support (3.8.0)
+    super_awesome_print (0.2.5)
+      awesome_print
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  bundler (>= 1.17)
+  pry
+  rake (>= 10.0)
+  rspec (>= 3.0)
+  super_awesome_print
+  typerb!
+
+BUNDLED WITH
+   1.17.1
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..5670f84
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2018 Oleg Antonyan
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f96926f
--- /dev/null
+++ b/README.md
@@ -0,0 +1,43 @@
+# Typerb
+
+Welcome to your new gem! In this directory, you'll find the files you need to be able to package up your Ruby library into a gem. Put your Ruby code in the file `lib/typerb`. To experiment with that code, run `bin/console` for an interactive prompt.
+
+TODO: Delete this and the text above, and describe your gem
+
+## Installation
+
+Add this line to your application's Gemfile:
+
+```ruby
+gem 'typerb'
+```
+
+And then execute:
+
+    $ bundle
+
+Or install it yourself as:
+
+    $ gem install typerb
+
+## Usage
+
+TODO: Write usage instructions here
+
+## Development
+
+After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
+
+To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/typerb. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](http://contributor-covenant.org) code of conduct.
+
+## License
+
+The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).
+
+## Code of Conduct
+
+Everyone interacting in the Typerb project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/[USERNAME]/typerb/blob/master/CODE_OF_CONDUCT.md).
diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..b7e9ed5
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,6 @@
+require "bundler/gem_tasks"
+require "rspec/core/rake_task"
+
+RSpec::Core::RakeTask.new(:spec)
+
+task :default => :spec
diff --git a/bin/console b/bin/console
new file mode 100755
index 0000000..bcb3d83
--- /dev/null
+++ b/bin/console
@@ -0,0 +1,14 @@
+#!/usr/bin/env ruby
+
+require "bundler/setup"
+require "typerb"
+
+# You can add fixtures and/or initialization code here to make experimenting
+# with your gem easier. You can also use a different console, if you like.
+
+# (If you use this, don't forget to add pry to your Gemfile!)
+require "pry"
+Pry.start
+
+#require "irb"
+#IRB.start(__FILE__)
diff --git a/bin/setup b/bin/setup
new file mode 100755
index 0000000..dce67d8
--- /dev/null
+++ b/bin/setup
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here
diff --git a/lib/typerb.rb b/lib/typerb.rb
new file mode 100644
index 0000000..a7461ad
--- /dev/null
+++ b/lib/typerb.rb
@@ -0,0 +1,21 @@
+require 'typerb/version'
+
+module Typerb
+  refine Object do
+    def type!(*klasses)
+      raise ArgumentError, 'provide at least one class' if klasses.size < 1
+
+      unless klasses.any? { |kls| self.is_a?(kls) }
+        where = caller_locations(1,1)[0]
+        file = where.path
+        line = where.lineno
+        code = File.read(file).lines[line - 1].strip
+        node = RubyVM::AST.parse(code)
+        var_name = node.children.last.children.first.children.first
+
+        kls_text = klasses.size > 1 ? "#{klasses.map(&:name).join(' or ')}" : klasses.first.name
+        raise TypeError, "`#{var_name}` should be #{kls_text}, not #{self.class}"
+      end
+    end
+  end
+end
diff --git a/lib/typerb/version.rb b/lib/typerb/version.rb
new file mode 100644
index 0000000..56fe700
--- /dev/null
+++ b/lib/typerb/version.rb
@@ -0,0 +1,3 @@
+module Typerb
+  VERSION = '0.1.0'
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
new file mode 100644
index 0000000..b44917a
--- /dev/null
+++ b/spec/spec_helper.rb
@@ -0,0 +1,15 @@
+require 'bundler/setup'
+require 'typerb'
+require 'super_awesome_print'
+
+RSpec.configure do |config|
+  # Enable flags like --only-failures and --next-failure
+  config.example_status_persistence_file_path = '.rspec_status'
+
+  # Disable RSpec exposing methods globally on `Module` and `main`
+  config.disable_monkey_patching!
+
+  config.expect_with :rspec do |c|
+    c.syntax = :expect
+  end
+end
diff --git a/spec/typerb_spec.rb b/spec/typerb_spec.rb
new file mode 100644
index 0000000..56a0c38
--- /dev/null
+++ b/spec/typerb_spec.rb
@@ -0,0 +1,90 @@
+RSpec.describe Typerb do
+  it 'has a version number' do
+    expect(Typerb::VERSION).not_to be nil
+  end
+
+  it 'has RubyVM::AST' do
+    expect(RubyVM::AST.parse('1 + 2').children.size).to eq(3)
+  end
+
+  it 'raises TypeError for wrong type' do
+    kls = Class.new do
+      using Typerb
+
+      def initialize(arg)
+        arg.type!(Integer)
+        @arg = arg
+      end
+    end
+    expect { kls.new('hello') }.to raise_error(TypeError, '`arg` should be Integer, not String')
+    expect { kls.new(123) }.not_to raise_error
+  end
+
+  it 'works with multiple arguments' do
+    kls = Class.new do
+      using Typerb
+
+      def initialize(arg1, arg2, arg3)
+        arg1.type!(Numeric)
+        arg2.type!(String)
+        arg3.type!(Hash)
+      end
+    end
+    expect { kls.new('hello', 1, {}) }.to raise_error(TypeError, '`arg1` should be Numeric, not String')
+    expect { kls.new(1, 123, {}) }.to raise_error(TypeError, '`arg2` should be String, not Integer')
+    expect { kls.new(1, '123', nil) }.to raise_error(TypeError, '`arg3` should be Hash, not NilClass')
+    expect { kls.new(123, 'hello', { o: 1 }) }.not_to raise_error
+  end
+
+  it 'raises TypeError for wrong type and ugly syntax' do
+    kls = Class.new do
+      using Typerb
+
+      def initialize(arg)
+        arg.                type!(Integer)
+        # NOTE cannot split into multiline, i.e. this will not work
+        # arg.
+        #    type!(Integer)
+        @arg = arg
+      end
+    end
+    expect { kls.new('hello') }.to raise_error(TypeError, '`arg` should be Integer, not String')
+    expect { kls.new(123) }.not_to raise_error
+  end
+
+  it 'works with multiple classes' do
+    kls = Class.new do
+      using Typerb
+
+      def initialize(arg)
+        arg.type!(Integer, String)
+        @arg = arg
+      end
+    end
+    expect { kls.new(123) }.not_to raise_error
+    expect { kls.new('123') }.not_to raise_error
+    expect { kls.new({}) }.to raise_error(TypeError, '`arg` should be Integer or String, not Hash')
+  end
+
+  it 'raises ArgumentError if no classes given' do
+    kls = Class.new do
+      using Typerb
+
+      def initialize(arg)
+        arg.type!
+        @arg = arg
+      end
+    end
+    expect { kls.new('hello') }.to raise_error(ArgumentError, 'provide at least one class')
+  end
+
+  it 'does not work without refinement' do
+    kls = Class.new do
+      def initialize(arg)
+        arg.type!(Integer)
+        @arg = arg
+      end
+    end
+    expect { kls.new(1) }.to raise_error(NameError)
+  end
+end
diff --git a/typerb.gemspec b/typerb.gemspec
new file mode 100644
index 0000000..295bda5
--- /dev/null
+++ b/typerb.gemspec
@@ -0,0 +1,32 @@
+lib = File.expand_path('../lib', __FILE__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
+require 'typerb/version'
+
+Gem::Specification.new do |spec|
+  spec.name          = 'typerb'
+  spec.version       = Typerb::VERSION
+  spec.authors       = ['Oleg Antonyan']
+  spec.email         = ['oleg.b.antonyan@gmail.com']
+
+  spec.summary       = %q{Typecheck sugar for Ruby.}
+  spec.description   = %q{Typecheck sugar for Ruby.}
+  spec.homepage      = 'https://github.com/olegantonyan/typerb'
+  spec.license       = 'MIT'
+
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
+    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+  end
+  spec.bindir        = 'exe'
+  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ['lib']
+
+  spec.add_development_dependency 'bundler', '>= 1.17'
+  spec.add_development_dependency 'rake', '>= 10.0'
+  spec.add_development_dependency 'rspec', '>= 3.0'
+  spec.add_development_dependency 'super_awesome_print'
+  spec.add_development_dependency 'pry'
+
+  spec.required_ruby_version = '>= 2.6.0-preview3'
+end