the arc of software bends towards understanding
Hello loyal readers: Inside 206-105 has a new theme! I’m retiring Manifest, which was a pretty nice theme but (1) the text size was too small and (2) I decided I didn’t really like the fonts, I’ve reskinned my blog with a theme based on Brent Jackson’s Ashley, but ported to work on Wordpress. I hope you like it, and please report any rendering snafus you might notice on older pages. Thanks!
Today, I’d like to talk about some of the core design principles behind type classes, a wildly successful feature in Haskell. The discussion here is closely motivated by the work we are doing at MSRC to support type classes in Backpack. While I was doing background reading, I was flummoxed to discover widespread misuse of the terms “confluence” and “coherence” with respect to type classes. So in this blog post, I want to settle the distinction, and propose a new term, “global uniqueness of instances” for the property which people have been colloquially referred to as confluence and coherence.