ezyang’s blog

the arc of software bends towards understanding


Idiomatic algebraic data types in Python with dataclasses and Union

One of the features I miss most in non-Haskell programming languages is algebraic data types (ADT). ADTs fulfill a similar role to objects in other languages, but with more restrictions: objects are an open universe, where clients can implement new subclasses that were not known at definition time; ADTs are a closed universe, where the […]

  • October 14, 2020

Rapidly prototyping scripts in Haskell

I’ve been having some vicious fun over the weekend hacking up a little tool called MMR Hammer in Haskell. I won’t bore you with the vagaries of multimaster replication with Fedora Directory Server; instead, I want to talk about rapidly prototyping scripts in Haskell—programs that are characterized by a low amount of computation and a […]

  • October 18, 2010

Keyword arguments in Haskell

Keyword arguments are generally considered a good thing by language designers: positional arguments are prone to errors of transposition, and it’s absolutely no fun trying to guess what the 37 that is the third argument of a function actually means. Python is one language that makes extensive use of keyword arguments; they have the following […]

  • September 13, 2010

Bug boogie: Git and symlinks

Git is very careful about your files: unless you tell it to be explicitly destructive, it will refuse to write over files that it doesn't know about, instead giving an error like: Untracked working tree file 'foobar' would be overwritten by merge. In my work with Wizard, I frequently need to perform merges on working […]

  • June 2, 2010

Mutation sleuthing in Python

Python is a language that gives you a lot of rope, in particular any particular encapsulation scheme is only weakly enforced and can be worked around by a sufficiently savvy hacker. I fall into the "my compiler should stop me from doing stupid things" camp, but I'll certainly say, dynamic capabilities sure are convenient. But […]

  • March 19, 2010

Writing generator friendly code

I've come a long ways from complaining to the html5lib list that the Python version gratuitously used generators, making it hard to port to PHP. Having now drunk the laziness kool-aid in Haskell, I enjoy trying to make my code fit the generator idiom. While Python generators have notable downsides compared to infinite lazy lists […]

  • March 1, 2010