Finding Clojure

Finding Clojure

Kurt Harriger @kurtharriger

The Challenge

Twitter search url filter

Project Folder
% lein new twitturl
Created new project in: /Users/kurtharriger/code/twitturl

├── README
├── project.clj
├── src
│ └── twitturl
│ └── core.clj
└── test
└── twitturl
└── test
└── core.clj

% git init && git add -A && git commit -m “create project”

project.clj
(defproject twitturl "1.0.0-SNAPSHOT"
:description "Twitturl aggregator"
:dependencies [[org.clojure/clojure "1.2.0"]
[org.clojure/clojure-contrib "1.2.0"]
[ring "0.3.7"]
[clj-http "0.1.2"]]
:dev-dependencies [[lein-ring "0.4.0"]]
:ring {:handler twitturl.core/app})

Appleholics
% brew install leiningen

Non Appleholics
Find Leiningen for Clojure on
https://github.com/technomancy/leiningen
% lein self-install

S-Expressions
Clojure:
(defn fn [arg1 & more] arg1)

defn is a macro used here with 3 parameters:
function name, arguments, and body.
Returns the function binding.

Clojure:
(println (fn value1 value2))

Java:
System.out.println(fn(value1, value2));

ring framework
(ns twitturl.core
(:require [com.twinql.clojure.http :as http])
(:use [ring.middleware.params])
(:use [hiccup.core]))

Import dependencies

(defn handler [] nil) ;todo create handler

(def app (-> handler wrap-params))

-> operator used apply multiple
Entry point functions to handler

De-structuring
(defn format-tweets [json] nil) ; todo

(defn handler [{{q "q"} :params}]
{ :content-type "text/html"
:body (html [:body
(-> (search q) format-tweets)])})

same as: Only need q

(defn handler [request]
(let [params (request :params) Local variable assignments
q (params "q")] request and params
{:content-type "text/html" unnecessary.
:body (html [:body
(-> (search q) format-tweets)])}))

The Search
(def url "http://search.twitter.com/search.json")

define readonly variable named url

(defn search [query]
(http/get url :query {:q query} :as :json))

returns result of com.twinql.clojure.http.get
using parameter list
1) url
2) :query
3) {:q query }
4) :as
5) :json

Enter the repl
% lein deps
Copying 22 files to /Users/kurtharriger/code/twitturl/lib
Copying 17 files to /Users/kurtharriger/code/twitturl/lib/dev

% lein repl
REPL started; server listening on localhost:24319.
user=> (use ‘twitturl.core)
nil
user=> (search “clojure”)

{:code 200,
:reason "OK",
:content
{:results
[{:from_user "planetclojure",
:text "Removing defined tests in Clojure REPL
http://goo.gl/fb/qeUty #clojure #SO",
...
}, ...]
}
}

The Handler
(defn format-tweets [json] nil) ; todo

(defn handler [{{q "q"} :params}]
{ :content-type "text/html"
:body hiccup library function

(html [:body
(-> (search q) format-tweets)])})

same as (format-tweets (search q))

returns a map containing
:content-type and :body

functions
(defn aslink [url]
(html [:a {:href url} url]))
user=> (aslink “http://url1”)
"<a href="http://url1">http://url1</a>"

(def urls (partial re-seq #"http://S+"))
same as:
(defn urls [text] (re-seq #“http://S+” text))

user=> (urls “blah blah http://url1 http://url2”)
("http://url1" "http://url2")

map reduce
(defn linkify [text]
(reduce #(.replace %1 %2 (aslink %2))
text (urls text)))
(fn [newText url]
(.replace newText url (aslink url))

String linkify(String text) {
String newText = text;
for(String url : getUrls(text)) {
newText = newText.replace(url, asLink(url));
}
return newText;
}

chaining
(defn format-tweet [tweet] 1 2
[:li (:from_user tweet)
[:blockquote (-> tweet :text linkify)]])

Java:

linkify(tweet.get(“text”))

chaining
(defn format-tweet [tweet] 1 2 2
[:li (:from_user tweet)
[:blockquote (-> tweet :text linkify)]])

Java:

linkify(tweet.get(“text”))
4

Java requires more(parentheses)?!

chaining
(defn format-tweets [json]
[:ul (->> json :content :results
(remove #(-> % :text urls nil?))
(map format-tweet))])
ArrayList<String> formatTweets(JSONObject json) {
StringBuilder tweets = new StringBuilder();
tweets.append(“<ul>”);
JSONObject content = json.getJSONObject(“content”);
JSONArray results = json.getJSONArray(“results”);
for(JSONObject tweet : results) {
String[] urls = getUrls(tweet.getString(“text”))
if(urls != null && urls.length > 0) {
tweets.append(“<li>” + formatTweet(tweet) “</li>”);
}
}
tweets.append(“</ul>”);
return tweets;
}

chaining
(defn format-tweets [json] 5
[:ul (->> json :content :results
(remove #(-> % :text urls nil?))
(map format-tweet))])
ArrayList<String> formatTweets(JSONObject json) {
StringBuilder tweets = new StringBuilder();
tweets.append(“<ul>”);
JSONObject content = json.getJSONObject(“content”);
JSONArray results = json.getJSONArray(“results”);
for(JSONObject tweet : results) {
12
String[] urls = getUrls(tweet.getString(“text”))
if(urls != null && urls.length > 0) {
tweets.append(“<li>” + formatTweet(tweet) “</li>”);
}
}
Java usually requires more(parentheses)?!
tweets.append(“</ul>”);
return tweets;
}

ring server
% lein ring server
2011-04-16 21:18:54.965:INFO::Logging to STDERR via org.mortbay.log.StdErrLog

2011-04-16 21:18:54.968:INFO::jetty-6.1.26

2011-04-16 21:18:54.998:INFO::Started SocketConnector@0.0.0.0:3000

Started server on port 3000

% lein ring war
Created /Users/kurtharriger/code/twitturl/twitturl-1.0.0-SNAPSHOT.war

Amazon Elastic Beanstalk plugin
https://github.com/weavejester/lein-beanstalk

src/twitturl/core.clj
1 (ns twitturl.core
2 (:use [ring.middleware.params])
3 (:use [hiccup.core])
4 (:require [com.twinql.clojure.http :as http]))
5
6 (def url "http://search.twitter.com/search.json")
7
8 (defn search [query] (http/get url :query {:q query} :as :json))
9 (defn aslink [url] (html [:a {:href url} url]))
10
11 (def urls (partial re-seq #"http://S+"))
12
13 (defn linkify [text]
14 (reduce #(.replace %1 %2 (aslink %2)) text (urls text)))
15
16 (defn format-tweet [tweet]
17 [:li (:from_user tweet)
18 [:blockquote (-> tweet :text linkify)]])
19
20 (defn format-tweets [json]
21 [:ul (->> json :content :results
22 (remove #(-> % :text urls nil?))
23 (map format-tweet))])
24
25 (defn handler [{{q "q"} :params}]
26 { :content-type "text/html"
27 :body (html [:body (-> (search q) format-tweets)])})
28
29 (def app (-> handler wrap-params ))

Finding Clojure
https://github.com/kurtharriger/twitturl
Leiningen Ring framework

DSLs Lists are awesome

Less () than Java De-structuring

Method chaining High-order functions

Kurt Harriger @kurtharriger

Finding Clojure

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