Divergent

A collection of monads for handling error in ruby.

Installation

Add this line to your application’s Gemfile:

gem 'divergent'

And then execute:

$ bundle

Or install it yourself as:

$ gem install divergent

Usage

Using Try:

require 'divergent'

include Divergent

require 'uri'
def parse_url(url)
  Try {
    URI.parse url
  }
end

success_url = parse_url("http://www.google.com") # => Success<http://www.google.com>

failed_url = parse_url(':google.com') #=> Failure<bad URI(is not URI?): :google.com>

### get_or_else

failed_url.get_or_else URI('http://duckduckgo.com') #=> #<URI::HTTP http://duckduckgo.com>

### chainable operations

# map
success_url.map(&:scheme) #=> Success<http>

failed_url.map(&:scheme) #=> Failure<bad URI(is not URI?): :google.com>

# fmap
parse_url("http://thisisnotagoodsite.com").fmap do |url|
  Try { Net::HTTP.get(url) }
end

# each
parse_url("http://google.com").each { |url| p url.to_s }
# =>
# "http://google.com"

# filter
parse_url("http://google.com").filter { |url| url.scheme == "http" }  #=> Success<http://google.com>
parse_url("http://google.com").filter { |url| url.scheme == "https" } #=> Failure<Predicate does not hold for http://google.com>

# recover from error
failed_url.recover(NoMethodError) { |error|
  :no_method
}.recover(StandardError) { |error|
  :standard_error
} #=> Success<standard_error>

Try { 1 / 0 }.recover(ZeroDivisionError, &:message)

Maybe has similar interface to Try.
Maybe uses None instead of Failure.

# provide default value
user = Maybe(User.find('a_non_exist_id'))
user.get_or_else(default_user)
user.or_else Maybe(User.find_by_name("username"))

# usage as a collection
user.each { |u| p u}
user.map(&:age)
user.fmap { |u| Maybe(u.gender) }
user.filter { |u| u.age > 20 }

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/lerencao/divergent.rb.

License

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