Duncan Coutts, from Well-Typed, gave a tech talk on Tuesday, 7th Oct, 10.30am, at Galois, about the technical direction of Cabal, Haskell package infrastructure, and the problems of managing large volumes of Haskell code. (.pdf slides).
This will be an informal talk and discussion on two topics:AbstractA language for build systemsBuild systems are easy to start but hard to get right. We’ll take the view of a language designer and look at where our current tools fall down in terms of safety/correctness and expressiveness.We’ll then consider some very early ideas about what a build system language should look like and what properties it should have. Currently this takes the form of a design for a build DSL embedded in Haskell.Constraint solving problems in package deploymentWe are all familiar, at least peripherally, with package systems. Every Linux distribution has a notion of packages and most have high level tools to automate the installation of packages and all their dependencies. What is not immediately obvious is that the problem of resolving a consistent set of dependencies is hard, indeed it is NP-complete. It is possible to encode 3-SAT or Sudoku as a query on a specially crafted package repository.We will look at this problem in a bit more detail and ask if the right approach might be to apply our knowledge about constraint solving rather than the current ad-hoc solvers that most real systems use. My hope is to provoke a discussion about the problem.