Multimethods: mars 2013

tisdag 26 mars 2013

Don'ts: Git hooks as CI/deploy tool

GIҬ

I want to get Heroku-like functionality for deploying new version - just git push and you're done. Crazy sexy cool.

I did try with git hooks in various ways, but since I run the server as a nohup jetty-process (I know) and have to kill that in brutal ways, cannot be sure on the merging of the branches since I had the git repo checked out (use a intermediate bare repo, please) I could not get it work. It was also really hard to know what was happening.

The search light is now against lein-war (for running in tomcat7) and some nice pallet solution.\

Git hooks is awesome for other things, but they are no system deployment/ continuous integration tool.

Update: I'm now a happy Jenkins user. Easy to get started with!

fredag 22 mars 2013

merge-with to the rescue

I'm working on coloring a map with different colors, that sometimes overlap.

After deep though I found out that I could have colorings in maps and then merge the maps somehow. This doesn't work perfectly, but it's a good start. After fiddling around with home-brewed solutions I looked in core.clj for merge in the source code and found merge-with just below. Perfect match.

A short example of the power of merge-with:

(def scandinavia (zipmap ["sweden" "norway" "denmark" "aaland" "iceland" "finland" "greenland" "fareoes"] (repeat :yellow)))
=>{"fareoes" :yellow, ...

(def swedish-speaking (zipmap ["sweden" "aeland" "finland" "ukraine" ] (repeat :red)))
=>{"ukraine" :red, ... * see below for Swedish language in Ukraine

(defn blend [a b] :orange)

(merge-with blend scandinavia swedish-speaking)

{"ukraine" :red,
"fareoes" :yellow,
"greenland" :yellow,
"finland" :orange,
"iceland" :yellow,
"aaland" :orange,
"denmark" :yellow,
"norway" :yellow,
"sweden" :orange}

As you can I cheated quite extensively with the blend function, but in this case it doesn't matter, since we're always blending yellow and red if we are blendning.

Merge-with uses the function given (blend) if two keys are colliding when merging. If you want to sum to maps, use (merge-with + {:x 1 :y 2} {:x 3}) and get {:x 4 :y 2}.

* And yes, there are some really old ladies speaking Swedish in Ukraine in the Gammalsvenskby.

torsdag 21 mars 2013

Minimal C2 bind! example

C2 is a very sane vizualisation library for both Clojure and ClojureScript.

I had a hard time grasping bind! and unify, so I wanted to make the smallest example I could think of: generate a blue svg circle.

From O'Reilly's excellent introduction to SVG (available online) I found that the XML for an SVG circle would be something like:

<svg width="400px" height="400px">
<circle cx="100" cy="100" r="45" style="fill: 'blue';"/>
</svg>

I did once spend unreasonably long time to try to reach the DOM of an embedded SVG image, so from now on I embed the SVG DOM root in my html document, like this document with an empty SVG tag with id "bubbles":

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>SVG bubble</title>
</head>
<body>
<div>
<svg id="bubbles"></svg></div>
</div>
<script src="/cljscode.js"></script>
</body>
</html>

C2 transforms tags like Hiccup do, but you can say where you want to add it with the macro c2.util/bind! (works a bit like in enlive).

And some very minimal ClojureScript code:

(ns c2test.core
(:require [c2.core :as c2core])
(:require-macros [c2.util :as c2util]))

(defn ^:export c2bubble [x y r]
(c2util/bind! "#bubbles"
[:svg#bubbles {:style {:display "block" :margin "auto" :height 200 :width 200}}
[:circle {:cx x :cy y :r r :style { :fill "blue"}}]]))

By opening a browser console (for javascript) I can set coordinates of a blue bubble with a command like

c2test.core.c2bubble(20,50,30);

Now on to world domination.

onsdag 20 mars 2013

Logging in Clojure

There are several competing logging facilities in Java and some custom made for Clojure.

If you are starting a new project, consider to simply use Logback. There's an bloggpost introduction to integrate logback with Clojure and it's github repo clojure-example-logback-integration.

This took me too long to figure out.