README.md in rubype-0.0.1 vs README.md in rubype-0.1.0

@@ -1,31 +1,116 @@
-# Rubype
+# Ruby with Type.
 
-TODO: Write a gem description
+Matz has mentioned Ruby3.0 with static type at some confluences. But almost all rubyists(include me) are not sure how typed Ruby is.
 
-## Installation
+But it's worth thinking more. This gem is kind of trial without so much side-effect.
 
-Add this line to your application's Gemfile:
+```rb
+require 'rubype'
 
+# ex1
+class MyClass
+  def sum(x, y)
+    x + y
+  end
+  type Numeric, Numeric >= Numeric, :sum
+
+  def wrong_sum(x, y)
+    'string'
+  end
+  type Numeric, Numeric >= Numeric, :sum
+end
+
+MyClass.new.sum(1, 2)
+#=> 3
+
+MyClass.new.sum(1, 'string')
+#=> ArgumentError: Wrong type of argument, type of "str" should be Numeric
+
+MyClass.new.wrong_sum(1, 2)
+#=> TypeError: Expected wrong_sum to return Numeric but got "str" instead
+
+# ex2: (Ruby 2.1.0+)
+class MyClass
+  type Numeric, Numeric >= Numeric, def sum(x, y)
+    x + y
+  end
+
+  type Numeric, Numeric >= Numeric, def wrong_sum(x, y)
+    'string'
+  end
+end
+
+# ex3: (Ruby 2.1.0+)
+class People
+  type People >= Any, def marry(people)
+    # Your Ruby code as usual
+  end
+end
+
+People.new.marry(People.new)
+#=> no error
+
+People.new.marry('non people')
+#=> ArgumentError: Wrong type of argument, type of "non people" should be People
+```
+
+## Feature
+### Typed method can coexist with non-typed method
+
 ```ruby
-gem 'rubype'
+# It's totally OK!!
+class MyClass
+  def sum(x, y)
+    x + y
+  end
+  type Numeric, Numeric >= Numeric, :sum
+
+  def wrong_sum(x, y)
+    'string'
+  end
+end
 ```
 
-And then execute:
+### Duck typing
 
-    $ bundle
+```ruby
 
-Or install it yourself as:
+class MyClass
+  def foo(any_obj)
+    1
+  end
+  type Any >= Numeric, :foo
+end
 
-    $ gem install rubype
+# It's totally OK!!
+MyClass.new.foo(1)
+# It's totally OK!!
+MyClass.new.foo('str')
+```
 
-## Usage
+## Installation
 
-TODO: Write usage instructions here
+gem install rubype or add gem 'rubype' to your Gemfile.
 
-## Contributing
+This gem requires Ruby 2.0.0+.
 
-1. Fork it ( https://github.com/[my-github-username]/rubype/fork )
-2. Create your feature branch (`git checkout -b my-new-feature`)
-3. Commit your changes (`git commit -am 'Add some feature'`)
-4. Push to the branch (`git push origin my-new-feature`)
-5. Create a new Pull Request
+### Contributing
+
+Fork it ( https://github.com/[my-github-username]/rubype/fork )
+
+Create your feature branch (`git checkout -b my-new-feature`)
+
+    $ bundle install --path vendor/bundle
+
+Commit your changes (`git commit -am 'Add some feature'`)
+
+    $ bundle exec rake test
+
+    > 5 runs, 39 assertions, 0 failures, 0 errors, 0 skips
+
+Push to the branch (`git push origin my-new-feature`)
+
+Create a new Pull Request
+
+## Credits
+[@chancancode](https://github.com/chancancode) first brought this to my attention. I've stolen some idea from him.