result.rb

module Result

  def Result.capture
    begin
      Ok.new(yield)
    rescue StandardError => e
      Error.new(e)
    end
  end

end

module ResultMethods

  def map
    handle_result(
      Proc.new {|val| Ok.new(yield(val)) },
      Proc.new {|err| self })
  end

  def join
    handle_result(
      Proc.new {|val| val },
      Proc.new {|err| self })
  end

  def flat_map
    map {|x| yield(x) }.join
  end

  def map_safe
    handle_result(
      Proc.new {|val| Result::capture { yield(val) } },
      Proc.new {|err| self })
  end

  def flat_map_safe
    map_safe {|x| yield(x) }.join
  end

end


class Ok

  include ResultMethods

  def initialize(result)
    @result = result
  end

  def to_s
    "Ok.new(#{@result.to_s})"
  end

  def handle_result(success_handler, failure_handler)
    success_handler.call(@result)
  end

end

class Error

  include ResultMethods

  def initialize(err)
    @err = err
  end

  def to_s
    "Error.new(#{@err.to_s})"
  end

  def handle_result(success_handler, failure_handler)
    failure_handler.call(@err)
  end

end