Ruby example of caller specified callback

callback.rb

require 'ostruct'
require 'open-uri'
require 'json'

class TemperatureApiError < StandardError
end

class CheeError < StandardError
end

DEFAULT_FALLBACK = ->(error) { raise }

def get_temp(query, &fallback)
  fallback ||= DEFAULT_FALLBACK
  key  = ENV['WUNDERGROUND_KEY']
  url  = "http://api.wunderground.com/api/#{key}/conditions/q/#{query}.json"
  data = open(url).read
  JSON.parse(data)['current_observation']['temp_f']
rescue => error
  fallback.call(error)
end

# get_temp("00000") => defaults to the DEFAULT_FALLBACK

# get_temp("00000") do |error|
# 	raise TemperatureApiError, error.message
# end

tst = ->(error) { raise TemperatureApiError, error.message }
get_temp("00000", &tst)