A problem that has plagued my GHC installation for a while is that whenever I tried to install any non-trivial package I would get a horrible link error like this:

I recently tracked down the cause of the persistent “thread blocked indefinitely in an MVar operation” exceptions I was getting from the GHC runtime when I used my parallel-io library. There doesn’t seem to be much information about this exception on the web, so I’m documenting my experiences here to help those unfortunate souls that come across it.

A little-known feature of GHC is the ability to run a program (that has been compiled with profiling) with the +RTS -xc option. Now, every time an exception is raised a stack trace will be dumped to stderr. This is the only way get stack traces for your Haskell code currently. Unfortunately:

I seem to have been fairly consistent at using my Twitter account, so look there if you want information about my latest projects (there are lots of them!) that is updated more frequently than this blog.

I spent Saturday at the TEDxCam Hackathon. This was an event which got together more than 40 coders to work in teams on a project in the area of data visualisation to compete for gadgets and tickets to the main conference.