Saturday, April 19, 2014

Building opencv java module

Last week I tried to build OpenCV java module so I could use it for clj-drone so I could have more fun with AR Drone 2.0.  I couldn't figure out why the java module is set unavailable after cmake.  This happens on both Ubuntu 12.04 and OS X 10.9.  I have seen some issues regarding properly setting the JAVA_HOME and the cmake JNI file being incorrect.  I tried to look at this angle, seeing why the JNI interface would not work.

However it seems "ant" is a required component and not just a recommended install as indicated by the docs.  So after a "brew install ant" and "apt-get install ant" cmake is able to properly set the Java OpenCV module.  I never had ant for years in my system, right now only using mvn, sbt and lein.

OpenCV 2.4.5 built just fine on Ubuntu, OSX seems to be having some c++ compile issue...

Thursday, April 3, 2014

Learning Clojure by doing a simple things

I usually tinker around different languages or technology.  I have been learning a bit of Clojure for the last couple of weeks.  Tried it at the office, by making a simple REST client.  Now just making a simple web app, just to get a feel of the language and ecosystem around it.

Clojure reminds me of Tcl, I know its LISP and it should remind more of emacs.  It reminds me of Tcl as I done a lot of Tcl programming using aolserver and OpenACS before.  Unlike the first few times I used Ruby or Scala, where the first wow factor is the language.  Tcl and Clojure the wow factor is getting to do something really quick.  They both have quirky syntax, but simple and uniform.

Here is why I am learning Clojure:
  • Learning a new languages makes me better at the languages I already know.  Getting the nice feeling of being new, and learning a lot on the way... mistakes and aha moments.
  • Still on my journey to be a better Functional Oriented hipster.  Not that I am leaving Object Oriented or even procedural away, just learning a another way of thinking and solving computing issues.
  • Getting my son to learn something.  Clojure seems to have nice abstraction for sql, web and js.  Start with 1 language will be less intimidating, instead of learning a lot in 1 bang.
As a newbie, I started with a framework first.  I like get to know other people's opinion first before making my own.  I picked Luminus as it seem to be using some of things that the clojure community is using.  Here are some code snippets from bottom layer to top.  Its simple and lacks any real world complications yet, learn the ropes on the basic things first.

Data using Korma

It starts with a macro for defining an entity and I would guess the convention to tie with the backing rdbms tables.  Then you define some functions using Korma's sql dsl.  You deal with primarily 2 data structure "id" which is a string and "product" which is a map.

Web using Ring and Compojure

The above is defining the routes, which you tie to the application handler.  Real nice bits are the ability to define a context.  Which would mean enclosing routes will start with that path first.  Easy way to extract the request body from a key ":body-params", and to respond with body by setting the key ":body".

Finally the front end using Clojurescript, Gyr and Angular.js

It looks less Clojure idiomatic, however I wanted to start somewhere.  Angular.js is familiar to me, just realised that its been about 2 years ago I started looking at Angular.js.  We have been using it ever since, I am actually rusty on it already.  I saw the Gyr and Putnam project had pretty good documentation.  Gyr gives some macros such as def.factory, def.controller, etc.  which looks similar to normal angular.  Then the ability to use $ which is pretty nice.  You will need to use "obj" and "arr" to interact with normal Javascript objects and arrays.

Clojure is nice and simple (still on first impression).  Gets you up and running quick.  If its good for long big projects, I don't know yet.  However I will be happy if I can meet 2 out of my 3 objectives in learning Clojure.  Complete source code here for the curious.