Result

Installation

Add this line to your application's Gemfile:

gem 'result-monad'

And then execute:

$ bundle

Or install it yourself as:

$ gem install result-monad

Usage

Use of the Result Monad is a paradigm that is baked into Rust and can lead to very good error handling. This is an initial design, and will need to be refined. The Capture() constructor makes it quite easy to integrate Result into a preexisting code base.

Examples

Capture success into an Ok result, and exceptions into an Error result via

Capture { 100 / 10 } #=> Result<Ok(10)>

Capture { 100 / 0 } #=> Result<Error(divided by 0)>

Construct Ok or Error yourself

  def can_go_wrong
    res = do_operation
    if res.meets_expectations
      Ok(res)
    else
      Error(res)
    end
  end

Basic Dichotomy

def divide(x, y)
  Capture { x / y }
end

x = divide 50, 10 #=> Result<Ok(5)>
x.ok? #=> true
x.error? #=> false

y = divide 50, 0 #=> Result<Error(divided by 0)>
y.error? #=> true
y.ok? #=> false

Chaining computations with map

x = Ok(100)

x.map {|i| i / 10}
 .map {|i| i / 5}
 .map {|i| i / 1}
#=> Result<Ok(2)>

Carrying errors through computations

x = Ok(100)

x.map {|i| i / 10}
 .map {|i| i / 0}
 .map {|i| i / 10}

#=>Error(divided by 0)

Dealing with nested results

x = Ok(100)

x.map {|i| Ok(i / 2)}
#=> Ok(Ok(50))

x.map {|i| Ok(i / 2)}.join
#=> Ok(50)

y = Ok(10)

y.flat_map {|i| Ok(i/ 2)}
#=> Ok(5)

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.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/result. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.