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/presentations/2010-06-13-functional-techniques-in-ruby/index.html

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  68. <div id="slides" class="offscreen" style="display:none;">
    69. 

  69. <div class="slide" data-transition="none"><div class="content" ref="1_intro/1_title">
    70. 

  70. <h1>functional techniques in ruby</h1>
    71. 

  71. 

  72. <h2>a pecha-kucha-like talk</h2>
    73. 

  73. 

  74. <h3>by: bradley grzesiak</h3>
    75. 

  75. 

  76. <h3>aka: <a href="//twitter.com/listrophy">@listrophy</a></h3></div>
    77. 

  77. </div><div class="slide" data-transition="none"><div class="content" ref="1_intro/2_functional_vs_imperative">
    78. 

  78. <h1>functional v. imperative</h1>
    79. 

  79. 

  80. <p><img src="./file/func.png" alt="Functional Diagram" style="float: left; margin-left: 10px"/></p>
    81. 

  81. 

  82. <p><img src="./file/imperative.png" alt="Imperative Diagram" style="float: right; margin-right: 10px"/></p></div>
    83. 

  83. </div><div class="slide" data-transition="none"><div class="content" ref="1_intro/3_a_digression">
    84. 

  84. <h1>a digression into the past</h1>
    85. 

  85. 

  86. <pre><code>10 REPEAT "after me"
    87. 

  87. 20 DO !use("gotos")
    88. 

  88. 30 GOTO 20
    89. 

  89. </code></pre></div>
    90. 

  90. </div><div class="slide" data-transition="none"><div class="content" ref="2_states/1_just_as_bad">
    91. 

  91. <h1>what's just as bad?</h1>
    92. 

    93. 

  93. <pre class="sh_ruby"><code>'foobar'.gsub! /oo/, 'u'
    94. 

  94. 

  95. %x[date 0314]
    96. 

  96. 

  97. product.save</code></pre></div>
    98. 

  98. </div><div class="slide" data-transition="none"><div class="content bullets" ref="2_states/2_state_vs_result">
    99. 

  99. <h1>state vs. result</h1>
    100. 

  100. 

  101. <ul>
    102. 

  102. <li>imperative :: change state of environment</li>
    103. 

  103. <li>functional :: take input(s) to produce output(s)</li>
    104. 

  104. </ul>
    105. 

  105. </div>
    106. 

  106. </div><div class="slide" data-transition="none"><div class="content" ref="2_states/3_ick">
    107. 

  107. <h1>ick</h1>
    108. 

  108. 

  109. <pre class="sh_ruby"><code>def grade(score)
    110. 

  110.   the_grade = nil
    111. 

  111.   if score &gt; 90 then the_grade = 'A'
    112. 

  112.   elsif score &gt; 80 then the_grade = 'B'
    113. 

  113.   else the_grade = 'U'
    114. 

  114.   the_grade
    115. 

  115. end</code></pre></div>
    116. 

  116. </div><div class="slide" data-transition="none"><div class="content" ref="2_states/4_moar_betta">
    117. 

  117. <h1>moar betta</h1>
    118. 

  118. 

  119. <pre class="sh_ruby"><code>def grade(score)
    120. 

  120.   score &gt; 90 ? 'A' :
    121. 

  121.     (score &gt; 80 ? 'B' : 'U')
    122. 

  122. end</code></pre></div>
    123. 

  123. </div><div class="slide" data-transition="none"><div class="content bullets" ref="3_higher_order_functions/1_higher_order_functions">
    124. 

  124. <h1>higher order functions</h1>
    125. 

  125. 

  126. <h2>or functions that can:</h2>
    127. 

  127. 

  128. <ul>
    129. 

  129. <li>take functions as arguments</li>
    130. 

  130. <li>return functions</li>
    131. 

  131. </ul>
    132. 

  132. </div>
    133. 

  133. </div><div class="slide" data-transition="none"><div class="content" ref="3_higher_order_functions/2_complement">
    134. 

  134. <h1>complement</h1>
    135. 

  135. 

  136. <div style="text-align: right; font-size: 200%">NB: f[*a] == f.call(*a)</div>
    137. 

  137. 

  138. 

  139. <pre class="sh_ruby"><code>def complement f
    140. 

  140.   lambda {|*a| not f[*a]}
    141. 

  141. end
    142. 

  142. 

  143. is_even = lambda {|n| n % 2 == 0}
    144. 

  144. is_odd = complement(is_even)
    145. 

  145. is_odd[1] # true</code></pre></div>
    146. 

  146. </div><div class="slide" data-transition="none"><div class="content" ref="3_higher_order_functions/3_conjoin">
    147. 

  147. <h1>conjoin</h1>
    148. 

  148. 

  149. <pre class="sh_ruby"><code>def conjoin *e
    150. 

  150.   base = lambda {|*a| true}
    151. 

  151.   e.inject(base) do |c, pred|
    152. 

  152.     lambda do |*a|
    153. 

  153.       c[*a] &amp;&amp; pred[*a]
    154. 

  154.     end
    155. 

  155.   end
    156. 

  156. end</code></pre></div>
    157. 

  157. </div><div class="slide" data-transition="none"><div class="content" ref="3_higher_order_functions/4_conjoin_huh">
    158. 

  158. <h1>huh?</h1>
    159. 

  159. 

  160. <h2>values : all? :: functions : conjoin</h2>
    161. 

  161. 

  162. <pre class="sh_ruby"><code>is_number = lambda {|n| n.kind_of?(Numeric)}
    163. 

  163. is_even = lambda {|n| n % 2 == 0}
    164. 

  164. div_by_three = lambda {|n| n % 3 == 0}
    165. 

  165. 

  166. even_number_div_by_three =
    167. 

  167.   conjoin(is_number, is_even, div_by_three)</code></pre></div>
    168. 

  168. </div><div class="slide" data-transition="none"><div class="content" ref="3_higher_order_functions/5_conjoin_why">
    169. 

  169. <h1>ok... why?</h1>
    170. 

  170. 

  171. <pre class="sh_ruby"><code>def even_number_div_by_3 arg
    172. 

  172.   [(arg.kind_of?(Numeric)),
    173. 

  173.     (arg % 2 == 0), (arg % 3 == 0)].
    174. 

  174.       inject(true){|memo,res| memo &amp;&amp; res}
    175. 

  175. end</code></pre>
    176. 

  176. 

  177. <h2>What of:</h2>
    178. 

  178. 

  179. <pre class="sh_ruby"><code>even_number_div_by_3(Object.new)
    180. 

  180. # 'undefined method `%' for #&lt;Object:...&gt;</code></pre></div>
    181. 

  181. </div><div class="slide" data-transition="none"><div class="content smbullets" ref="3_higher_order_functions/6_library">
    182. 

  182. <h1>a library you might write</h1>
    183. 

  183. 

  184. <ul>
    185. 

  185. <li>complement</li>
    186. 

  186. <li>compose</li>
    187. 

  187. <li>conjoin</li>
    188. 

  188. <li>disjoin</li>
    189. 

  189. <li>filter</li>
    190. 

  190. <li>map</li>
    191. 

  191. <li>reduce</li>
    192. 

  192. <li>and a big one...</li>
    193. 

  193. </ul>
    194. 

  194. </div>
    195. 

  195. </div><div class="slide" data-transition="none"><div class="content smbullets" ref="3_higher_order_functions/7_map_reduce">
    196. 

  196. <h1>map-reduce</h1>
    197. 

  197. 

  198. <ul>
    199. 

  199. <li>map:
    200. 

  200. 

  201. <ul>
    202. 

  202. <li>[a, e, g] becomes:</li>
    203. 

  203. <li>{a =&gt; [b,c,d], e =&gt; [b,d,f], g =&gt; [b]}</li>
    204. 

  204. </ul>
    205. 

  205. </li>
    206. 

  206. <li>reduce:
    207. 

  207. 

  208. <ul>
    209. 

  209. <li>collapse the inverse:</li>
    210. 

  210. <li>{b =&gt; 3, d =&gt; 2, c =&gt; 1, f =&gt; 1}</li>
    211. 

  211. </ul>
    212. 

  212. </li>
    213. 

  213. <li>Add some smarts &amp; you get "Google PageRank"</li>
    214. 

  214. </ul>
    215. 

  215. </div>
    216. 

  216. </div><div class="slide" data-transition="none"><div class="content bullets" ref="4_conclusion/1_scale">
    217. 

  217. <h1>functional scales</h1>
    218. 

  218. 

  219. <ul>
    220. 

  220. <li>given input(s), you get output(s)</li>
    221. 

  221. <li>everything is self-contained</li>
    222. 

  222. <li>parallel processing FTfW</li>
    223. 

  223. </ul>
    224. 

  224. </div>
    225. 

  225. </div><div class="slide" data-transition="none"><div class="content bullets" ref="4_conclusion/2_bad_news">
    226. 

  226. <h1>the bad news</h1>
    227. 

  227. 

  228. <ul>
    229. 

  229. <li>tail recursion optimization is nice, but not in most ruby 1.8 implementations</li>
    230. 

  230. <li>more abstraction &#x2248;&gt; more confusion</li>
    231. 

  231. </ul>
    232. 

  232. </div>
    233. 

  233. </div><div class="slide" data-transition="none"><div class="content bullets" ref="4_conclusion/3_more">
    234. 

  234. <h1>more!</h1>
    235. 

  235. 

  236. <ul>
    237. 

  237. <li>currying: built into 1.9</li>
    238. 

  238. <li>lazy evaluation/memoization: "let" in RSpec</li>
    239. 

  239. <li>infinite streams: see sequences in FactoryGirl</li>
    240. 

  240. </ul>
    241. 

  241. </div>
    242. 

  242. </div><div class="slide" data-transition="none"><div class="content" ref="4_conclusion/4_blown">
    243. 

  243. <h1>phew!</h1>
    244. 

  244. 

  245. <h2>is your mind blown?</h2></div>
    246. 

  246. </div><div class="slide" data-transition="none"><div class="content smaller" ref="4_conclusion/5_neat">
    247. 

  247. <h1>also, this is neat</h1>
    248. 

  248. 

  249. <pre><code>!!! 5
    250. 

  250. %html
    251. 

  251.   %head
    252. 

  252.     %script(src='jquery.js')
    253. 

  253.     :javascript
    254. 

  254.       $(function(){ $('h1').click(function(){$.post('/');})});
    255. 

  255.     :css
    256. 

  256.       h1 { height: 100em }
    257. 

  257.   %body
    258. 

  258.     %h1 play
    259. 

  259. 

  260. %w(rubygems sinatra haml).map{|x|require x}
    261. 

  261. get('/'){haml :index}
    262. 

  262. post('/'){`osascript -e 'tell app "Keynote" to start slideshow'`}
    263. 

  263. </code></pre></div>
    264. 

  264. </div>
    265. 

  265. </div>
    266. 

  266. 

  267. </body>
    268. 

  268. </html>
    269. 

  269.