Cleanliness is Next to Domain-Specificity

Cleanliness is Next to
Domain-Specificity
Ben Scofield
Senior Developer
Viget Labs

4 November 2007
© Copyright 2007 Viget Labs, LLC – www.viget.com

Part 1: Linguistics
Part 2: Refactoring

http://www.flickr.com/photos/jesper/1395418767/

Interdisciplinary

Real DSLs

Ruby Domain-Specific Code

Same Grammar,
Different Vocabulary

DSLs
DSL

Intimidate
and
Frighten
http://www.ﬂickr.com/photos/cwsteeds/58514985/

Write a Parser?
No, Thanks.

http://www.ﬂickr.com/photos/rooreynolds/243810988/

http://www.ﬂickr.com/photos/jonosd/498162310/

Change the Vocabulary
Change the World

Heroes on NBC - Mondays at 9 PM

http://www.oreillynet.com/onlamp/blog/2006/05/
sapirwhorf_is_not_a_klingon.html
http://tech.puredanger.com/2006/11/08/does-your-programming-
language-affect-how-you-think/
http://snakesgemscoffee.blogspot.com/2006_11_01_archive.html
http://talklikeaduck.denhaven2.com/articles/2007/06/11/sapir-
whorf
http://adams.id.au/blog/2007/10/what-is-behaviour-driven-
development/
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/75914
http://www.weiqigao.com/blog/2007/09/10/
an_interesting_experiment_sapir_whorf_hypothesis.html
http://www.ibm.com/developerworks/blogs/page/pmuellr?
tag=ruby
http://intertwingly.net/blog/2007/10/05/NOC
http://brooders.net/category/perl/
http://gilesbowkett.blogspot.com/2007/02/sapir-worf-in-
action_19.html
http://blogs.msdn.com/daveremy/archive/2005/04/06/
sapirwhorfs.aspx
http://erlangish.blogspot.com/2007/05/shape-of-your-mind.html
http://www.oreillynet.com/onlamp/blog/2006/06/
how_does_a_programming_languag.html

http://www.flickr.com/photos/maxhunter/79993854/

Snow
qanuk avalanche
kaneq blizzard
kanevvluk dusting
natquik flurry
nevluk frost
aniu hail
qanikcaq hardpack
muruaneq igloo
nutaryuk pingo
qanisqineq powder
qengaruk sleet
utvak slush
navcaq snow
pirta snowflake
pirtuk snowstorm
... ...

Color
Perception

http://www.flickr.com/photos/thedeplorableword/140856437/

Direction of Causality
Degree of Influence

RSpec Leads You in
the Right Direction

DSDs are Built on
Linguistic Relativism

Keep Your Head in
the Domain

exit 0

@@results.each do |r|
if searchtype == 'h'
puts quot;#{r.price} url=#{r.url}quot;
puts quot;#{r.stars} #{r.name} $#{r.loprice} - $#{r.hiprice}quot;
elsif searchtype == 'f'
puts quot;#{r.price} url=#{r.url}quot;
r.legs.each do |leg|
puts quot; #{leg}quot;
end
end
end

exit(0)
more = poll_results_file(searchtype)
@@results.each do |r|
puts quot;#{r.price} #{r.url}quot;
r.legs.each do |leg|
puts quot; #{leg}quot;
end
end
end

Whoa.

I Want to:
find flights from CLT to RDU leaving today
and returning in one week

I Want to:
find :flights, :from => :CLT, :to => :RDU,
:leaving => Date.today, :returning => Date.today + 7

48
40

The Old Way
sid = getsession(@@token)
searchid = start_flight_search(sid, ‘n’, ‘CLT’, ‘RDU’, Date.today, nil, 1)

more = poll_results('f', sid, searchid, nil)
while more == 'true' do
more = poll_results('f', sid, searchid, nil)
sleep(3)
end

def poll_results(searchtype, sid, searchid, count)
url = quot;/s#{@@sparkleinstance}/apibasic/flight?searchid=#{searchid}&apimode=1&_sid_=#{sid}quot;

more = nil
Net::HTTP.start(@@hostname, @@port) do |http|
if count
url += quot;&c=#{count}quot;
end
response = http.get(url)
body = response.body
File.open(quot;ksearchbody.xmlquot;, quot;wquot;) do |f|
f.puts(body)
end
more = handle_results(searchtype, body)
if more != 'true'
# save the body, so we can test without doin
# an actual search
File.open(quot;ksearchresults.xmlquot;, quot;wquot;) do |f|
f.puts(body)
end
end
end
return more
end

48
40

The Old Way, cont.
def handle_results(searchtype, body)
xml = REXML::Document.new(body)
more = xml.elements['/searchresult/morepending']
@@lastcount = xml.elements['/searchresult/count'].text
@@sparkleinstance = xml.elements['/searchresult/searchinstance'].text
if more
more = more.text
end
if more != 'true'
@@results = []
#puts quot;count=#{@@lastcount}quot;
xml.elements.each(quot;/searchresult/trips/tripquot;) do |e|
trip = Trip.new()
e.each_element(quot;pricequot;) do |t|
trip.price = t.text
trip.url = t.attribute(quot;urlquot;)
end
e.each_element(quot;legsquot;) do |legs|
legs.each_element(quot;legquot;) do |l|
leg = Leg.new
l.each_element do |ld|
# extract the detail from each leg
case
when ld.name == 'airline': leg.airlinecode = ld.text
#...
end
end
trip.legs << leg
end # leg in legs loop
end # legs in trip loop
#e.each_element(quot;/searchresult/trips/trip/pricequot;) { |p| trip.price = p.text }
#puts quot;trip: #{trip.price}quot;
@@results << trip
end # each trip
end
return more
end

40

Output
session_url = quot;/k/ident/apisession?token=#{token}quot;

search_url = quot;/s/apisearch?basicmode=true&oneway=n&origin=#{origin}
&destination=#{destination}&destcode=&depart_date=#{dep_date}
&depart_time=a&return_date=#{ret_date}&return_time=a&travelers=#
{travelers}&cabin=e&action=doflights&apimode=1&_sid_=#{sid}quot;

results_url = quot;/s#{@@sparkleinstance}/apibasic/flight?searchid=#
{searchid}&apimode=1&_sid_=#{sid}quot;

40

Expectations
class KayakTest < Test::Unit::TestCase
def test_find_should_call_out_to_session_endpoint
setup_mocks_for_find
Kayak.find :flights
end

private
def setup_mocks_for_find
response = mock(:body => '<?xml version=quot;1.0quot;?>
<ident>
<uid>uid</uid>
<sid>0123456789</sid>
<token>12345</token>
<error></error>
</ident>')
success = mock()
success.expects(:get).with('/k/ident/apisession?token=12345').returns
(response)
Net::HTTP.expects(:start).at_least_once.yields(success)
end
end

40

Parsing Responses
class KayakTest < Test::Unit::TestCase
def test_session_response_should_be_parsed_for_session_id
setup_mocks_for_find
Kayak.find :flights
assert_equal '0123456789', Kayak.session_id
end

private
def setup_mocks_for_find
response = mock(:body => '<?xml version=quot;1.0quot;?>
<ident>
<uid>uid</uid>
<sid>0123456789</sid>
<token>12345</token>
<error></error>
</ident>')
success = mock()
success.expects(:get).with('/k/ident/apisession?token=12345').returns
(response)
Net::HTTP.expects(:start).at_least_once.yields(success)
end
end

class Kayak

First Cut
@@session_id = nil
@@search_id = nil
@@search_options = {}

TOKEN = '12345'
HOSTNAME = 'www.kayak.com'
PORT = 80

class << self
def session_id
@@session_id
end

def method_missing(name, *args)
@@search_options[name]
end

def find(type, conditions = {})
session_id ||= initialize_session
@@search_options[:origin] = conditions[:from]
@@search_options[:destination] = conditions[:to]
@@search_options[:depart_date] = conditions[:leaving].strftime('%m/%d/%Y') if conditions[:leaving]
@@search_options[:leave_date] = conditions[:returning].strftime('%m/%d/%Y') if conditions[:returning]

search_id ||= initialize_search
self
end

def initialize_search
Net::HTTP.start(HOSTNAME, PORT) do |http|
response = http.get(quot;/s/apisearch?basicmode=true&oneway=n&destcode=&depart_time=a&...
if body = response.body
@@search_id = xml.elements['//searchid'].text
end
end
end

def initialize_session
response = http.get(quot;/k/ident/apisession?token=#{TOKEN}quot;)
if body = response.body
@@session_id = xml.elements['//sid'].text
end
end
end
end
end

module Kayak

Second Cut
TOKEN = '12345'
HOSTNAME = 'www.kayak.com'
PORT = 80

class Flight
attr_accessor :session, :search_id, :search_options

def method_missing(name, *args)
search_options[name]
end

def initialize(conditions = {})
session ||= Kayak::Session.new
self.search_options = {}
self.search_options[:origin] = conditions[:from]
self.search_options[:destination] = conditions[:to]
self.search_options[:depart_date] = conditions[:leaving].strftime('%m/%d/%Y') if conditions[:leaving]
self.search_options[:return_date] = conditions[:returning].strftime('%m/%d/%Y') if conditions[:returning]

response = http.get(quot;/s/apisearch?basicmode=true&oneway=n&destcode=&depart_time=a&return_date=...
self.search_id = Kayak.retrieve(response, '//searchid')
end
end

def self.find(args)
self.new(args)
end
end

class Session
attr_accessor :session_id

def initialize
Net::HTTP.start(Kayak::HOSTNAME, Kayak::PORT) do |http|
response = http.get(quot;/k/ident/apisession?token=#{Kayak::TOKEN}quot;)
self.session_id ||= Kayak.retrieve(response, '//sid')
end
end
end

def self.find(type, *args)
case type
when :flights
Kayak::Flight.find(*args)
end
end

...

Optional Parentheses
looks like a sentence

Blocks for All
In other languages, you have to specify
explicitly that a function can accept another
function as an argument. But in Ruby, any
method can be called with a block as an
implicit argument.
Matz, 2003

Optional Braces
not that common

• Start Modestly
• Stay in the Domain
• Get Better

56

That’s It
travel safely

Cleanliness is Next to Domain-Specificity

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