Example for https://stackoverflow.com/q/67502628/477037

dsl-example.rb

class Client
  def self.post(&block)
    data = DslData.new
    Dsl.new(data).instance_eval(&block)

    # build request with data from dsl calls
    # and execute request
    puts "Making a request to #{data.url} with headers #{data.headers}"
    response = "response" # this would be your http response
    if rand > 0.5 # response.success?
      data.on_success.call(response) if data.on_success
    else
      data.on_error.call(response) if data.on_error
    end
  end
end

class DslData
  attr_accessor :url, :headers, :on_success, :on_error

  def initialize
    @headers = {}
  end
end

class Dsl
  def initialize(data)
    @data = data
  end

  def url(value)
    @data.url = value
  end

  def header(key, value)
    @data.headers[key] = value
  end

  def on_success(&block)
    @data.on_success = block
  end

  def on_error(&block)
    @data.on_error = block
  end
end

Client.post do |client|
  url "http://somewhere"
  header "Kwazy", "Cupcakes"
  on_success do |response|
    puts "got #{response} which is a success"
  end

  on_error do |response|
    puts "gor #{response} which is an error"
  end
end