Inside 245-5D

Existential Pontification and Generalized Abstract Digressions


Backpack for deep learning

This is a guest post by Kaixi Ruan. Backpack is a module system for Haskell, released recently in GHC 8.2.1. As this is a new feature, I wanted to know how people use it. So I searched Twitter every day, and the other day I saw this tweet: Are there other examples than String/Bytestring/Text? So […]

  • August 17, 2017

Proposal: Suggest explicit type application for Foldable length and friends

tl;dr If you use a Foldable function like length or null, where instance selection is solely determined by the input argument, you should make your code more robust by introducing an explicit type application specifying which instance you want. This isn't necessary for a function like fold, where the return type can cross-check if you've […]

  • March 21, 2017

Designing the Backpack signature ecosystem

Suppose you are a library writer interested in using Backpack. Backpack says that you can replace a direct dependency on a function, type or package with one or more signatures. You typecheck against a signature and your end user picks how they want to eventually implement the signature. Sounds good right? But there's a dirty […]

  • March 11, 2017

How to integrate GHC API programs with Cabal

GHC is not just a compiler: it is also a library, which provides a variety of functionality that anyone interested in doing any sort of analysis on Haskell source code. Haddock, hint and ghc-mod are all packages which use the GHC API. One of the challenges for any program that wants to use the GHC […]

  • February 8, 2017

Try Backpack: Cabal packages

This post is part two of a series about how you can try out Backpack, a new mixin package system for Haskell. In the previous post, we described how to use a new ghc --backpack mode in GHC to quickly try out Backpack's new signature features. Unfortunately, there is no way to distribute the input […]

  • January 17, 2017

A tale of backwards compatibility in ASTs

Those that espouse the value of backwards compatibility often claim that backwards compatibility is simply a matter of never removing things. But anyone who has published APIs that involve data structures know that the story is not so simple. I'd like to describe my thought process on a recent BC problem I'm grappling with on […]

  • December 31, 2016

Backpack and the PVP

In the PVP, you increment the minor version number if you add functions to a module, and the major version number if you remove function to a module. Intuitively, this is because adding functions is a backwards compatible change, while removing functions is a breaking change; to put it more formally, if the new interface […]

  • December 30, 2016

The problem of reusable and composable specifications

It's not too hard to convince people that version bounds are poor approximation for a particular API that we depend on. What do we mean when we say >= 1.0 && < 1.1? A version bound is a proxy some set of modules and functions with some particular semantics that a library needs to be […]

  • December 17, 2016

Thoughts about Spec-ulation (Rich Hickey)

Rich Hickey recently gave a keynote at Clojure/conj 2016, meditating on the problems of versioning, specification and backwards compatibility in language ecosystems. In it, Rich considers the "extremist" view, what if we built a language ecosystem, where you never, ever broke backwards compatibility. A large portion of the talk is spent grappling with the ramifications […]

  • December 16, 2016

Try Backpack: ghc --backpack

Backpack, a new system for mix-in packages in Haskell, has been released with GHC 8.2. Although Backpack is closely integrated with the Cabal package system, it's still possible to play around with toy examples using a new command ghc --backpack. Before you get started, make sure you have a recent enough version of GHC: ezyang@sabre:~$ […]

  • October 10, 2016