Experiment in Result#and_then in Ruby

and_then.rb

class Result
  def initialize(operation, failure_test, *args)
    @operation = operation
    @failure_test = failure_test
    @args = args
  end

  def and_then(next_operation)
    if failure_test.call(result)
      self
    else
      Result.new(next_operation, failure_test, result)
    end
  end

  def result
    @result ||= operation.call(*args)
  end

  private

  attr_reader :args, :failure_test, :operation
end

def failure
  puts "failure"
  { error: "Something went wrong" }
end

def success
  puts "success"
  { ok: 1 }
end

def increment(value)
  puts "increment"
  { ok: value[:ok] += 1 }
end

puts Result.new(proc { success }, proc { |resp| resp.key?(:error) }).
  and_then(proc { |val| increment(val) }).
  and_then(proc { |val| increment(val) }).
  and_then(proc { failure }).
  and_then(proc { |val| increment(val) }).
  result

This became https://github.com/tjmw/streamlet