Thoughts Heap

Vancouver's Clojure Club is ALIVE!

Wed, 01 Feb 2012 12:10:23 -0800

Some friends and myself decided to formalize a study group we were having for learning Clojure, at this point I think there is enough people that could comfortably work on open source projects.

The idea is to join and share projects as a group to gain more feedback from others, this way if a group checks and uses the libraries instead of individuals this libraries will definitely get more traction.

Hopefully this initiative will bring really great OS projects to life.

"Most of the biggest problems in software are problems of misconception."

Fri, 02 Dec 2011 09:57:43 -0800

“Most of the biggest problems in software are problems of misconception.”

- Rich Hickey.

Haskell's Show and pretty printing bad practice

Wed, 30 Nov 2011 06:02:06 -0800

Most of times when I was coding Haskell code, I always implemented the Show classtype whenever I wanted to print things on the screen in a nice and fashionable way.

It seems however this is a really bad practice that hasn’t been taught enough in the Haskell community. I discovered this in a StackOverflow question that had nothing to do with pretty printing, but the discussion led to that¹.

A user named Matt Fenwick suggested that for whatever reason the guy who asked the question shouldn’t implement the Show classtype, later on I started to comment:

Me: Why not declare Show classtype for the Expr? just curious?

hammar: Show is meant as a form of lightweight serialization. It’s not meant for pretty-printing, although people often abuse it that way. In particular, if a Read instance is also defined, one should be able to expect that read . show is the identity function.

After that realization, I went out and looked over for different pretty printing solutions in Haskell. This was quite frustrating, for some reason I didn’t find any library that would define pretty printing functions for basic containers like List, Set, Map.

The closest I’ve found to an out of the box pretty printing solution was the pretty-show package. However this doesn’t create a new classtype for pretty printing, making it really limiting IMO.

There is also the well established pretty package, This one provides combinators to create pretty printing functions easily, however, it doesn’t provide a classtype or a default implementation for the containers mentioned above.

Lastly the most promising package I’ve found is called GenericPretty. This one provides a classtype for pretty printing and implements some Prelude ADT, however no containers whatsoever and no combinators for generating pretty printing.

In conclusion, the pretty printing solutions are so, so… yet there is potential for something new raising up in the future.

¹ | Because of this the title was later changed to Show and Pretty-Printing

Clojure's repeatedly gotcha

Mon, 28 Nov 2011 07:05:00 -0800

When using Clojure’s repeatedly function to read lines from a terminal, or when trying to do IO of some sort, the behavior won’t be as expected

This is because repeatedly instead of calling the action n times, it generates a lazy seq for each time the action function gets called. Given that it is a lazy seq, if you don’t force the evaluation of the list, all but the first element will not be executed.

In order to avoid this, you have to use the dorun function, this is going to force evaluation for each element on a lazy seq, and it will discard the result of the seq altogether, this is because this function is expecting the action body to be for side-effects only

if you come from Haskell land, the idiom (dorun (repeatedly n body-fn)) would be the equivalent to call the function repeatM_.

An example:

Vim's Fugitive's "Error detected while processing function 51_Commit"

Tue, 08 Nov 2011 19:01:00 -0800

At a random time on my development cycle, I was using the awesome Fugitive plugin developed by Tim Pope, and I got the following strange error:


Error detected while processing function 51_Commit:
line   52:
E480: No match: `=msgfile`
Press ENTER or type command to continue

After some googling, I found out the reason was that I installed just a few days ago the also awesome ctrlp plugin. When you were setting up ctrlp, you did something like this:


set wildignore=*/.git/*,*/.hg/*,*/dist/*,*/cabal-dev/*

Well… it seems Fugitive plugin doesn’t like that very much, if you remove the git portion from that setting, Fugitive will work as expected again

Thanks Interwebz

"The distinction between mechanism and policy is one of the best ideas behind the Unix design. Most..."

Tue, 25 Oct 2011 14:52:54 -0700

“The distinction between mechanism and policy is one of the best ideas behind the Unix design. Most programming problems can indeed be split into two parts: “what capabilities are to be provided” (the mechanism) and “how those capabilities can be used” (the policy). If the two issues are addressed by different parts of the program, or even by different programs altogether, the software package is much easier to develop and to adapt to particular needs.”

- Jonathan Corbet, Greg Kroah-Hartman, Alessandro Rubini on Linux Device Drivers, 3rd Edition

chiguire: tejemaneje: Dennis Ritchie has just passed...

Thu, 13 Oct 2011 12:43:14 -0700

chiguire:

tejemaneje:

Dennis Ritchie has just passed away.

Surely you probably don’t know who this guy is, but his contributions to computer science made your life what it is right now.

Among other things, he created C, a programming language which is used to create all sort of OS and aplication software these days (and it will be that way in the future), and was key in the development of other important programming languages that came before. C made possible software as you know it.

Also, C was fundamental in the development of Unix, a OS that (one way or another) led to Linux. If you don’t want to mess with the Open Source / Licensed Software dilemma, keep in mind that Linux (and the Open Source movement in general) is a powerful engine that moves science and research nowadays.

In one week exactly the world has lost two of the greatest contributors in computer science. One dedicated to design, one dedicated to programming.

Maybe, if you allow me to put it that way, it is life saying us that both things are equally important.

Lo recordaremos hasta 2038.

Another Great One has gone…

Rest in peace dude… Thanks for the ride. Great men leave...

Wed, 05 Oct 2011 17:19:41 -0700

Rest in peace dude… Thanks for the ride. Great men leave young.

Testing URI canonicalization using QuickCheck

Thu, 29 Sep 2011 15:21:00 -0700

Today I was working on a custom web crawler for the company I’m working in. One of the problems I was having in the first implementations was that I was not canonicalizing the links, and I was visiting the same link more than once in the crawl.

Canonicalization of URI’s basically consist on removing any query string and fragment out of the given URI (at least, that is my understanding of canonicalization).

I needed to test a function that was doing the canonicalization of links, and decided to use a QuickCheck property to check just that. I implemented an Arbitrary instance for a pair of URI Strings, so that I could get the canonicalized version and a version with a query string and/or fragment, and compare the two after the canonicalization algorithm I developed.

The following code shows the Arbitrary instance of a newtype called URIPair

The next one shows how this is being used in a QuickCheck property test

Finally the Main action

By using the Gen monad combinators, and a newtype for URIs, I was able to implement in around 50 LOC, a generator for both canonicalized and normal links.

I’m still believing there must be a more elegant and shorter way to do this, or maybe I could reuse some code on Arbitrary instances for URIs, sadly no luck so far.

If you are Haskell developer yourself and want to provide insights, please fork the gist and show us how this can be done in a better way.

Cheers.

Puppet: ERROR 400 on SERVER: Must pass 'param-name' to Class['class-name']

Fri, 23 Sep 2011 14:16:00 -0700

I’m currently playing with puppet doing some changes to my modules to support Archlinux, at this time I did several changes to my git module, Initially the implementation was something like this:

And then, it became something like this:

In the end I added some new parameters to my git class, and changed my nodes.pp file accordingly:

For some crazy reason, the puppet agent was throwing me the following error:

err: Could not retrieve catalog from remote server: Error 400 on SERVER: Must pass user to Class[Git] at /etc/puppet/modules/git/manifests/init.pp:1 on node vagrantup.dev

Which was pretty annoying, given that I was passing all the parameters that the module was asking for. After two hours of trying in and out, reading documentation, doing magic incantations, etc. I decided to do this to my nodes.pp manifest file:

That miraculously solved the problem, Class inclusion order is important, even if the documentation doesn’t say so. This is as in puppet 2.7.3

"Don’t, Please don’t install puppet 2.7.3 with Ruby 1.9.2 ever, a freaking..."

Thu, 22 Sep 2011 17:30:00 -0700

“Don’t, Please ***don’t*** install puppet 2.7.3 with Ruby 1.9.2 ever, a freaking afternoon can be spent on that!”

- Me.

Thanks to this guy for pointing me in the right direction.

Stupid puppet and stupid ruby 1.9.2

Loading package double-conversion- ... : can't load .so/.DLL for: stdc++ (libstdc++.so: cannot open shared object file: No such file or directory)

Tue, 20 Sep 2011 20:52:00 -0700

Recently I’ve been playing with the aeson library in Ubuntu oneiric, unfortunately I ran across this compilation error:


Loading package double-conversion-0.2.0.1 ... : can't load .so/.DLL for: stdc++ (libstdc++.so: cannot open shared object file: No such file or directory)

After a lot of investigation, I found a ticket on the Ttrac site of GHC that came up with a solution, I will summarize here so you don’t have to read the ticket yourself:

hvr:

If you are on a Ubuntu-like distribution and don’t mind exposing libstdc++.so you can link, you could symlink it to /usr/local/lib, e.g.
$ ln -vs $(gcc --print-file-name=libstdc++.so) /usr/local/lib/
`/usr/local/lib/libstdc++.so' -> `/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/libstdc++.so'
basvandijk:

Note to others: I needed to do a
sudo ldconfig
after this to update my cache

Hope this helps.

Crawler implementation in Haskell

Mon, 19 Sep 2011 11:34:15 -0700

Today at Noomii I was getting some new requirements for our crawler that is implemented in Ruby. The requirement list was quite dense, and I was wondering if it was a good idea to implement this functionality in Haskell :-).

Later, after finishing the morning scrum meeting, I got my hands on Bryan O’Sullivan’s slides from the StrangeLoop conference, I was really interested in checking them out, given that I’m looking for better approaches to teach Haskell myself at the Vancouver unMeetup. What a surprise when I see an implementation of a Crawler on the presentation, the timing is so perfect it just makes me wonder is fate.

If you are a Haskell aficionado you will find this presentation pretty entertaining

When you know you like a language, you just know…

Aníbal Rojas: Como ser un mejor programador (un guía libre de pendejadas)

Sun, 18 Sep 2011 19:29:46 -0700

Aníbal Rojas: Como ser un mejor programador (un guía libre de pendejadas):

anibalrojas:

Yo no soy un gram programador, creo que nunca lo he sido, aunque por mucho años me dedicara a programar profesionalmente. No me entiendan mal, no es que no me guste programar ni que mi código apestte, en realidad me gusta mucho y he tenido muy buenos momentos programado, pero el trabajo no me deja…

Great post by one of my menthors back in Venezuela, hopefully at some point he will translate it.

"Elegance and familiarity are orthogonal"

Sun, 18 Sep 2011 13:25:26 -0700

“Elegance and familiarity are orthogonal”

- Rich Hickey (author of Clojure)

Meaning: Unless you are familiar with a concept/language etc, you are not able to tell if something is elegant or not.

"All the adversity I’ve had in my life, all my troubles and obstacles, have strengthened..."

Fri, 16 Sep 2011 19:32:17 -0700

“All the adversity I’ve had in my life, all my troubles and obstacles, have strengthened me… You may not realize it when it happens, but a kick in the teeth may be the best thing in the world for you.”

- Walt Disney.

Personal note: On the hardest times, just remember this.

Using and Parsing Dates in Haskell

Fri, 16 Sep 2011 19:10:39 -0700

Recently I’ve been playing around with the Github API, and I wanted to do some code using Haskell. I’ve been using several libraries like aeson, enumerator, http-enumerator, among others.

One of the details I was really concerned about was the time structures in Haskell, I didn’t know exactly which module to use, and there were at least two options:

After investigating a little bit about each, I settled down with Data.Time.Clock. The main reason to use it, was because this is the lib that Bryan O’Sullivan uses in his aeson library, and by seeing how he used it, I discovered how to parse dates from Strings easily in Haskell; using the Data.Time.Format, one has utility methods to parse strings into UTCTime. I did some handy code to parse the dates out of the Github api like so: I really recommend reading the aeson library, is one of a kind.

Do yourself a favor...

Mon, 29 Aug 2011 14:02:19 -0700

Never compile ghc-platform… ever, it took me around 12 hours to finish compilation, not fun at all.

Adrian Bravo's tumblr: Creating a Vagrant Base Box for Ubuntu

Mon, 29 Aug 2011 13:55:34 -0700

Adrian Bravo's tumblr: Creating a Vagrant Base Box for Ubuntu:

This is for me so that I don’t forget how to build vagrant boxes again…

"Any fool can write code that computers can understand. Good programmers write code that humans can..."

Wed, 24 Aug 2011 10:23:00 -0700

“Any fool can write code that computers can understand. Good programmers write code that humans can understand”

-
Martin Fowler (via edgar)