Trevor McDonell gave a presentation about the Accelerate Haskell library, which provides an EDSL for writing code which is compiled and executed on the GPU.
The approach involves using an EDSL to write CUDA code in a Haskell program. This is generates code to be compiled and shipped to the GPU at run time. Being Haskell, there’s a bunch of nice types involved: matrices have shapes, matrix and scalar programs/fragments are of different types, and there are a few of typeclasses.
Trevor demonstrated a brute-force MD5 collision finder written with Accelerate which was very impressive.
Mark Hibberd spoke about interpreters and little languages with the Free
package. Essentially, this boiled down to using Free with its functor and
monad instances to replace an API full of IO a typed operations, each of
them possibly unsafe, with a nice monadic EDSL and a single IO interpreter
function.
The various operations in the API no longer “do” the operation but build up a data structure describing the operations to be performed as a little data structure (essentially an AST) which the client code passes to an evaluation function.
The more advanced theory categories and groups and left adjoint functors and such left me behind, but his running example of a password manager library (to generate, store and retrieve passwords) very illuminated the practical side of using this technique. I’m quite looking forward to Jed Wesley-Smith’s YOW! Lambda Jam talk about a similar topic: Connection Management, FP Style: A Case Study.