Just pasting here / code by https://github.com/thoferon

gistfile1.rb

class Monad
  attr_reader :value

  def bind(f)
    raise "not implemented"
  end

  def self.return(v)
    self.new v
  end

  def initialize(value)
    @value = value
  end

  def self.construct(monad, *methods)
    if methods.empty?
      monad
    else
      construct(monad.bind(methods.first),
                *methods[1..-1])
    end
  end
end

class ReachedLimit < Monad
  def self.bind(f)
    ReachedLimit
  end
end

class Result < Monad
  def bind(f)
    result = f.call self.value
    result > 1000 ? ReachedLimit : Result.new(result)
  end
end


def twice(a)
  2 * a
end

def plus100(a)
  100 + a
end

def times4(a)
  4 * a
end

def times200(a)
  200 * a
end

# irb(main):009:0> Monad.construct(Result.return(1.1), method(:twice), method(:times200), method(:plus100), method(:twice))
# => ReachedLimit
# irb(main):010:0> Monad.construct(Result.return(1.1), method(:twice), method(:plus100), method(:twice))
# => #<Result:0x1065003f0 @value=204.4>