option.rb

class NoSuchElementException < StandardError; end

class Option
  def initialize(val)
    @val = val
  end

  def present?
    !@val.nil?
  end

  def map(&block)
    if present?
      Option(block.call(@val))
    else
      Option(nil)
    end
  end

  def flat_map(&block)
    if present?
      block.call(@val)
    else
      Option(nil)
    end
  end

  def get_or_else(fallback)
    present? ? @val : fallback
  end

  def to_s
    if present?
      "#<Option: Some(#{@val})>"
    else
      "#<Option: None>"
    end
  end
end

def Option(val)
  Option.new(val)
end

Some = -> (val) { val.present? }
None = -> (val) { !val.present? }





opt = Option(2)
case opt
when Some
  puts "opt had a present val!"
when None
  puts "opt was a blank val"
end

nil_opt = Option(nil)
case nil_opt
when Some
  puts "wat"
when None
  puts "nil_opt was a blank val"
end


puts Option(2).get_or_else(3)   # => 2
puts Option(nil).get_or_else(3) # => 3

puts Option(2).map { |x| x * 2 }              # => #<Option: Some(4)>
puts Option(2).flat_map { |x| Option(x * 2) } # => #<Option: Some(4)>

puts Option(nil).map { |x| x * 2 }              # => #<Option: None>
puts Option(nil).flat_map { |x| Option(x * 2) } # => #<Option: None>