Today I decided to embark on an exploration of Haskell web development. I have previously bootstrapped a basic Snap setup but never got into actual hacking. Today I decided to give Yesod a go. I ran into a number of difficulties that drained away all my spare time this evening but in the end I feel like I’m ready to dive in tomorrow.

I started off by attempting to install Yesod, with a simple cabal install yesod. This command took about 10 minutes to finish compiling dependencies on my ThinkPad X61 before it died with an error. The problem seemed to be the version of haskell-platform was rather out-of-date, meaning a tool, called alex was too old for Yesod. To solve this rather small issue I took the rather drastic step of upgrading Ubuntu on the ThinkPad to Precise Pangolin because this includes the latest haskell-platform…and its all new and…just because! This is Ubuntu after all - trigger happy upgrades are the name of the game.

Meanwhile, in Mac land. While that upgrade was running I tried to run the new yesod web app on a Mac. Unfortunately I ran into all the problems I’ve encountered before with cabal-dev on OS X.

Firstly there’s some weirdness with cabal-dev being set to install everything in the system library location. This just makes no sense for cabal-dev - the whole point is for it to install libraries in a vendored, per-project location - not interfering with system libraries. It manifested itself as asking for a password all the time (turn on verbose -v3 to see it running all cabal commands with sudo

• O_o). To fix that you edit the config file, outlined in a blog post I found. Annoying.

Another problem I had was ghc/ld spamming the terminal with loads of linker warnings. This really slowed down compilation. I didn’t really solve this (happened on my Mac Mini - didn’t happen on my work MacBook Air). I remember having to set options for GHC to silence that crap, but I forget the details…

In order to get it all working on my Mac I:

• Uninstalled haskell-platform (this is homebrew installed for me)
• Re-installed haskell-platform
• cabal installed cabal-dev, yesod

Everything worked then. There’s also strange voodoo you have to run to unregister old packages - brew info haskell-platform splits out the necessary commands.

After all that, things worked…mostly. Currently there seems to be some car crash of dependencies caused by a new release of something called tls-extras. A helpful stranger in IRC (#yesod) told me to cabal-dev install tls-extra-0.4.2.1 - this forces a working version of that library and then you can happily install yesod and everything’s groovy.

Who said Haskell was difficult? Not me.

So now I have a skeleton Yesod project up and running and it’s all looking very promising. The helper script for creating projects gave me some confidence - specifically asking if I wanted sqlite, postgres, MongoDB or nothing seemed pretty good to me - this doesn’t appear to be a web framework/persistence system tied to a particular way of doing things.

The main reason why I decided to dive into Yesod however was the high volume of interesting yesod-related blog traffic - this is a pretty crucial metric in gauging the health of a library community in my opinion and my RSS reader has been bombarded with posts about it so I felt I had to see what all the fuss was about.

Hopefully happy Haskell hacking henceforth