Recently, I have found myself leading a Haskell programming meet-up in Santa Fe, New Mexico. We meet downtown at HQ or at Desert Dogs, Mondays around 6pm. This meet-up has been a great opportunity to actually learn to program Haskell well. In an effort to archive our work as a group, I am publishing meet-up notes here.

Having a reliable test framework is an amazing thing. Here is a brief collection of notes describing some of the features and organizational structure of the `Haskell Test Framework`​ (HTF). Most of the examples are designed for my recent work developing a ray tracing algorithm.

### Listable.

Here we write some methods for treating Integers as lists in the sense that
we can define notions of` take, drop, (:), (++), and unit `on Integers. From these we derive further functionality, namely:` length, reverse, head, tail, and (!!)`. Since clearly both Integers and Lists are both instances of the same functionality, we define a class Listable handling both.

### Sortable.

Now that there is a Listable class, we extend Listable things to be Sortable things. Put another way, given `(Ord a, Listable a) => a` we define a class whose instances can be sorted via `sort` and shuffled via `shuffle`. The sort is a quick-sort and the shuffle is a key-shuffle.

### Vector.

Vector is a module designed to facilitate mathematical vector operations in the hermitian-style. For simplicity, I model only 3 dimensional vectors but allow the underlying fields to be arbitrary. Complex and Double serve as example fields throughout.

### Abelian Actions on a Zipper.

The goal here is to write an `Action` class which depends on an `Abelian` data type
and acts on a `Zipper` type. Composition of left Abelian actions `Ab x G -> G` and
evaluation are then given in the instance declaration for `Action (Zipper v)`.

### Havel Hakimi Graphs.

The Swiss-McMahon tournament can be seen as a special case of the Erdős–Gallai theorem and as such, the Havel-Hakimi algorithm can be used to produce graphic tournaments. This module is designed to facilitate the production of these graphs.

### Umeboshi – A Haskell Drum Machine.

Umeboshi is a drum machine written in Haskell and built from a Roland 808 sound bank. The drum machine is designed to facilitate poly-rhythmic percussion in non-standard time signatures. It relies heavily `Unboxed Vector` types and the `Data.WAVE` library.