I frequently have to "import" data from one database to another in order to get on with more interesting work, a process sometimes ingloriously referred to as "ETL: Extract, Transform, Load". Usually this must be done in some programming language already established at an organization, such as Python or Scala. However, in developing a library […]


What is defunctionalization? I recently gave a little demonstration entitled "What is Defunctionalization?" for UCSC TWIGS (the acronym, stolen from a similar seminar in the the U. Mass. math department, stands for The "What Is … ?" Graduate Seminar). The inspiration for this talk was just to present what I’d learned after Conor McBride’s brilliant […]

The call is out for submissions to the next issue of The Monad.Reader! To get an idea of the content (and because D Stewart told us all to read every past issue) I cracked open Issue 10, which has a nice tutorial by B Pope on the GHCi debugger. But having just finished a post […]

As an exercise, since my reading group was discussing model checking this week, I implemented the classic model checker for CTL specifications from the 1986 paper Automatic Verification of Concurrent Systems Using Temporal Logic Specifications by EM Clarke, EM Emerson, AP Sistla. The “efficient algorithm” presented in the paper is, upon reflection, merely […]

I’m reading the very fun Measure, Topology, and Fractal Geometry by GA Edgar, and thought I’d hack up some of the examples in Haskell. So this post implements cursor graphics in OpenGL in (I think) DSEL style, demonstrating the StateT and Writer monad gadgets from the standard library and a cool "novel representation of lists" […]

This is a question posed in my randomized algorithms class. If you are routing in a network whose connectivity looks "more or less" like a convex figure, what does the congestion look like? A quick way to make an educated guess is to draw a bunch of random line segments in such a convex shape […]

The Knuth-Bendix completion procedure (when it succeeds) transforms a collection of equations into a confluent, terminating rewrite system. Sometimes the procedure fails, and sometimes does not terminate, but The Handbook of Computational Group Theory by D Holt remarked that even in this case it generates an infinite set of rewrite rules that are complete, and […]

Any isometry of the plane has a unique normal form as the composition of a translation, rotation and reflection. This note computes this normal form and tests the implementation using the QuickCheck automated testing tool for Haskell. To generate random test data, I use another characterization of isometries as products of up to three reflections. […]

This note shows how to use OpenGL with Gtk in Haskell. The result is a little visualization to check our implementation of the classic iterative convex hull algorithm. This post is a valid literate Haskell file so save it to something like ConvexHull.lhs and compile with ghc –make ConvexHull. What you see above is what […]