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

The Ruby
Community

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

Linguistics

Categories

Regional Dialects

(more)
Regional
Dialects

Jargons Cants

Pidgins and Creoles

Vocabulary
Grammar

Real DSLs
Ruby Domain-Specific Code

ActiveRecord

RSpec

Same Grammar,
Different Vocabulary

Who Cares?

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

API vs. Dialect

Why DSanything?

Who Are We?

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

Linguistic Determinism

The Hopi

Linguistic Relativism

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

Sapir-Whorf

Testing is Too Late

Specifications
Come First

RSpec Leads You in
the Right Direction

DSDs are Built on
Linguistic Relativism

Keep Your Head in
the Domain

Refactoring

Tastes Vary

?

Finding a Ticket

kayak.com

What Does This Do?

Ruby? Awesome!

exit 0
@@results.each do |r|
if searchtype == 'h'
puts \"#{r.price} url=#{r.url}\"
puts \"#{r.stars} #{r.name} $#{r.loprice} - $#{r.hiprice}\"
elsif searchtype == 'f'
puts \"#{r.price} url=#{r.url}\"
r.legs.each do |leg|
puts \" #{leg}\"
end
end
end
exit(0)
more = poll_results_file(searchtype)
@@results.each do |r|
puts \"#{r.price} #{r.url}\"
r.legs.each do |leg|
puts \" #{leg}\"
end
end
end
Whoa.

Start at the End

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 = \"/s#{@@sparkleinstance}/apibasic/flight?searchid=#{searchid}&apimode=1&_sid_=#{sid}\"
more = nil
Net::HTTP.start(@@hostname, @@port) do |http|
if count
url += \"&c=#{count}\"
end
response = http.get(url)
body = response.body
File.open(\"ksearchbody.xml\", \"w\") 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(\"ksearchresults.xml\", \"w\") 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 \"count=#{@@lastcount}\"
xml.elements.each(\"/searchresult/trips/trip\") do |e|
trip = Trip.new()
e.each_element(\"price\") do |t|
trip.price = t.text
trip.url = t.attribute(\"url\")
end
e.each_element(\"legs\") do |legs|
legs.each_element(\"leg\") 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(\"/searchresult/trips/trip/price\") { |p| trip.price = p.text }
#puts \"trip: #{trip.price}\"
@@results << trip
end # each trip
end
return more
end

40
Output
session_url = \"/k/ident/apisession?token=#{token}\"
search_url = \"/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}\"
results_url = \"/s#{@@sparkleinstance}/apibasic/flight?searchid=#
{searchid}&apimode=1&_sid_=#{sid}\"

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=\"1.0\"?>
<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=\"1.0\"?>
<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(\"/s/apisearch?basicmode=true&oneway=n&destcode=&depart_time=a&...
if body = response.body
xml = REXML::Document.new(body)
@@search_id = xml.elements['//searchid'].text
end
end
end
def initialize_session
Net::HTTP.start(HOSTNAME, PORT) do |http|
response = http.get(\"/k/ident/apisession?token=#{TOKEN}\")
if body = response.body
xml = REXML::Document.new(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]
Net::HTTP.start(HOSTNAME, PORT) do |http|
response = http.get(\"/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(\"/k/ident/apisession?token=#{Kayak::TOKEN}\")
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
...

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

Third Cut
?

Always Room for
Improvement

Tips

:symbol
ignore the colon

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

Optional Parentheses
looks like a sentence

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

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

*
arrays from anything

Optional Braces
not that common

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

• Start Modestly
• Stay in the Domain
• Get Better

56
That’s It
travel safely

Ben Scofield
ben.scofield@viget.com
http://www.extendviget.com/
http://www.culann.com/
4 November 2007
© Copyright 2007 Viget Labs, LLC – www.viget.com