Some thoughts on hylang

I've been writing a couple of things in hy again this week. What's Hy? It's a cute idea. It's a lisp that compiles? (transpiles? I never get the difference) to the Python AST. I guess the elevator pitch might be something like clojure but for python. So yeah, a rich, super stable class-tree sort of OO language, with enormous portablility and twenty-odd years of library support for everything you might want to do, but with a nice, dynamic, lispy language and a repl.

I've played with hy a little bit on and off over the years. Actually, when I was working at SMR, I actually deployed some in production. (Somehow, I doubt that's still a thing). Python is my go-to scripting language, because it's very plain, very portable, batteries included, somewhat modern, probably already installed everywhere I work. I try to use it for scripty things, rather than shell or perl or something. Lisps are my favourite programming language. I just like how it fits together. I know lots of people don't, and I'm fine with that, but I always enjoy it.

So over the holiday weekend I found myself wanting a couple of almost throwaway scripts, and I decided to reach back into the hy bucket, and give that another try. I wrote a script to grab my selfie tweets from a twitter archive, and a rough script to publish formatted micro-blog entries directly from the shell.

It was a fun exercise. Hy has moved on a bit since I last tried. (They seem to have removed let, and car, and cdr, and lambda which I feel funny about), but by and large it works really well.

Things I like

  • I like mapping over lists of things, and in straight Python this is often clumsy and leads to densely nested comprehensions
  • actual lambdas!
  • Python3 support ( hy3 )
  • easy importing of python modules
  • mostly seamless python interop
  • repl works great
  • the repl shows you the pythonic syntax of the forms it evaluates, which is helpful if you know Python
  • emacs mode (obv)
  • it has lazy sequences
  • and multimethods!
  • it is fun to work in

Things I like less

  • Missing some olde lisp things like car/cdr/lambda
  • Things often expect you to be using methods on stateful objects, which gets you an OO impedance mismatch (I have the same problems in scala and clojure)
  • Slightly more typed than you expect, whilst not really offering you a type system. (Particularly with distinctions between lists, sequences, iterators.)
  • it often seems easier to imperative loop with for than map / reduce / filters, and this seems weird.
  • i don't feel I have any understanding about setv variable scoping.
  • no STM, which I think is one of the most interesting things about clojure
  • I don't think the error handling does restarts and conditions and things


I don't think I would choose to use it to build any complicated systems. (Typically this is true of Python as well to be fair). I'd love to see something like an idomatic web framework in it. I could imagine using it to build serverless workers over something like apex up or chalice perhaps. I should totally try that!

I am not really very good at it yet, so I doubt I'm writing optimal programs. My scripts often look like Dr. Moreau designs halfway between a python script and something more lispy. This could well improve as I understand the underlying sequence / itertools glue a bit more, I'm often routing around confusing sequenced things. I absolutely enjoy writing little scripts like this in it, and I think I maybe enjoy it more than I would if I was writing plain python. I gave some thought about why this might be and I think I figured it out.

It could just be as simple as being all about the code editing. Python, and it's whitespace delimited blocks, is fine, and super readable, but it's always slightly fiddly to edit. Some of this is my toolchain, I'm sure. There's a lot of bells and whistles you can glue over emacs for Python work, and they're pretty good, but I do always find it a slightly fiddly experience. Balanced expressions and sexprs though are obviously an absolute joy to edit in emacs, alongside an embedded inferior lisp repl, and although it's nowhere near as integrated an experience as using slime with a "real" lisp, it's closer to that than editing Python ever feels, and for me that's a significant productivity win. So I think it will stay in the toolbox.

I recommend Hy to anyone who is interested in interesting lightweight languages, especially scripting languages. Obviously it's particularly relevant to anyone who likes python or lisps, even if just as a curiosity. If you work with Python and like using emacs though, and like the sound of 'Python but with structured editing' I would strongly recommend you look at how it might integrate into your workflow.

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