Existential Pontification and Generalized Abstract Digressions

## POPL

Last night, I returned from my very first POPL, very exhausted, and very satisfied. It was great putting faces to names, chatting with potential PhD supervisors (both from the US and in the UK), and reveling in the atmosphere. Highlights from my files: Tony Hoare, on being awarded the ACM SIGPLAN Programming Languages Achievement Award, […]

• January 28, 2012

## Modelling IO: MonadIO and beyond

The MonadIO problem is, at the surface, a simple one: we would like to take some function signature that contains IO, and replace all instances of IO with some other IO-backed monad m. The MonadIO typeclass itself allows us to transform a value of form IO a to m a (and, by composition, any function […]

• January 24, 2012

## monad-control is tricky

Editor's note. I've toned down some of the rhetoric in this post. The original title was "monad-control is unsound". MonadBaseControl and MonadTransControl, from the monad-control package, specify an appealing way to automatically lift functions in IO that take "callbacks" to arbitrary monad stacks based on IO. Their appeal comes from the fact that they seem […]

• January 23, 2012

## Mystery Hunt and the Scientific Endeavour

It can be hard to understand the appeal of spending three days, without sleep, solving what some have called “the hardest recreational puzzles in the world,”; but over this weekend, hundreds of people converged on the MIT campus to do just that, as part of MIT Mystery Hunt. To celebrate the finding of the coin, […]

• January 16, 2012

## Problem Set: The Codensity Transformation

Have you ever wondered how the codensity transformation, a surprisingly general trick for speeding up the execution of certain types of monads, worked, but never could understand the paper or Edward Kmett's blog posts on the subject? Look no further: below is a problem set for learning how this transformation works. The idea behind these […]

• January 7, 2012

## Why iteratees are hard to understand

There are two primary reasons why the low-level implementations of iteratees, enumerators and enumeratees tend to be hard to understand: purely functional implementation and inversion of control. The strangeness of these features is further exacerbated by the fact that users are encouraged to think of iteratees as sinks, enumerators as sources, and enumeratees as transformers. […]

• January 4, 2012