Lost in Technopolis

Temporary mirror of comonad.com

johnw — Wed, 19 Jun 2013 19:10:39 +0000

Until the Comonad Reader comes back online, I have a temporary mirror setup at http://comonad.newartisans.com. It’s a bit old (Sep 2012), but has some classics like “Free Monads for Less”. It is missing the “Algebra of Applicatives”, though, since I hadn’t run the mirror in a while.

Nightly builds of GHC HEAD for Ubuntu 12.04.2 LTS

johnw — Wed, 19 Jun 2013 01:32:34 +0000

Chatting with merijn on #haskell, I realized I have a file server running Ubuntu in a VM that’s idle most of the time, so I decided to set up a jenkins user there and make use of it as a build slave in the evenings. This means that at http://ghc.newartisans.com, you’ll now find nightly builds [...]

Nightly builds of GHC HEAD for OS X 10.8

johnw — Wed, 12 Jun 2013 22:35:44 +0000

Since mid-January, I’ve been running nightly builds of GHC on my Mac Pro for 10.8.x, 64-bit. I’ve decided to make these results publically downloadable here: http://ghc.newartisans.com. The installer tarballs are in dist, while the fulltest and nofib logs are in logs. According to Jenkins this build takes 8h15m minutes, so I figured this might save [...]

Three examples of problems with Lazy I/O

johnw — Mon, 13 May 2013 01:44:48 +0000

Problem 1: The source of exceptions is obscured main = getArgs >>= readFile . head >>= print . length Even though length is a pure function, this is where the I/O will happen (lazily), which means that is where any exceptions relating to I/O will get raised. Pure code should avoid raising exceptions, which this [...]

An experiment: shorter posts

johnw — Mon, 13 May 2013 01:43:46 +0000

I think one reason I’ve been avoiding posting to my blog lately is the time commitment of writing something of decent length. To get over this hump, I’m going to shift my focus to writing smaller little discoveries of things I find during my researches into Haskell and technology. Let’s see how that goes.

Getting Started with Lenses

johnw — Wed, 21 Nov 2012 22:28:39 +0000

The following is the first in a series of articles I hope to write as a gentle introduction to Edward Kmett’s excellent lens library. Control.Lens provides a composable way to access and modify sub-parts of data structures (where by modify I mean: return a new copy with that part changed). In this introduction I won’t [...]

Arrows are simpler than they appear

johnw — Sat, 20 Oct 2012 15:56:30 +0000

I have found that arrows in Haskell are far simpler than they might appear based on the literature. They are simply abstractions of functions. To see how this is practically useful, consider that you have a bunch of functions you want to compose, where some of them are pure and some are monadic. For example, [...]

Just discovered pxz

johnw — Thu, 06 Sep 2012 08:01:00 +0000

To show just how significant parallelized algorithms can be, today I discovered pxz, a parallelized version of the xz compression utility, which I use constantly. The proof is in the numbers: Command Before After Ratio Time xz 2937M 305M 0.104 32m pxz -9e 2937M 281M 0.096 4m(!) I put this alias in my .zshrc: alias [...]

Running a fully local Hoogle

johnw — Wed, 05 Sep 2012 03:09:58 +0000

Today I finally succeeded at getting a fully local version of Hoogle running on my machine, with filesystem links for all packages that I have installed, and remote links for those I don’t. Since this was definitely a non-trivial exercise, I wanted to capture the knowledge here for anyone else trying to do the same. [...]

The fix combinator and recursive lambdas

johnw — Mon, 03 Sep 2012 13:00:36 +0000

The fix combinator is a higher order function that can turn any function into a potentially recursive one. It can be a bit difficult to wrap your head around, since neither the definition nor the documentation is very clear on what you might use it for. However, I’ve found one handy use case: creating recursive [...]