jank development update - New projects!
May 31, 2024 · Jeaye Wilkerson

Hey folks! I've been building on last month's addition of lazy sequences, loop*, destructuring, and more. This month, I've worked on rounding out lazy sequences, adding more mutability, better meta support, and some big project updates. Much love to Clojurists Together, who are funding my work this quarter.

Chunked sequences

I've expanded the lazy sequence support added last month to include chunked sequences, which pre-load elements in chunks to aid in throughput. At this point, only clojure.core/range returns a chunked sequence, but all of the existing clojure.core functions which should have support for them do.

If you recall from last month, there is a third lazy sequence type: buffered sequences. I won't be implementing those until they're needed, as I'd never even heard of them before researching more into the lazy sequences in Clojure.

Initial quarter goals accomplished

Wrapping up the lazy sequence work, minus buffered sequences, actually checked off all the boxes for my original goals this quarter. There's a bottomless well of new tasks, though, so I've moved onto some others. So, how do I decide what to work on next?

My goal is for you all to be writing jank programs. The most important tasks are the ones which bring me closer to that goal. Let's take a look at what those have been so far.

Volatiles, atoms, and reduced

Most programs have some of mutation and we generally handle that with volatiles and atoms in Clojure. jank already supported transients for most data structures, but we didn't have a way to hold mutable boxes to immutable values. Volatiles are also essential for many transducers, which I'll mention a bit later. This month, both volatiles and atoms have been implemented.

Implementing atoms involved a fair amount of research, since lockless programming with atomics is not nearly as straightforward as one might expect.

As part of implementing atoms, I also added support for the @ reader macro and the overall derefable behavior. This same behavior will be used for delays, futures, and others going forward.

Meta handling for defs

Last quarter, I added support for meta hints, but I didn't actually use that metadata in many places. Now, with defs, I've added support for the optional meta map and doc string and I also read the meta from the defined symbol. This isn't a huge win, but it does mean that jank can start using doc strings normally, and that we can do things like associate more function meta to the var in a defn, which can improve error reporting.


There will be many jank projects and I've known for a while that I want them all to be in one git monorepo. This makes code sharing, searching, refactoring, and browsing simpler. It gives contributors one place to go in order to get started and one place for all of the issues and discussions. It's not my intention to convince you of anything, if you're not a fan of monorepos, but jank is now using one.

This started by bringing in lein-jank, which was initially created by Saket Patel. From there, I've added a couple of more projects, which I'll cover later in this update.

New clojure.core functions

Following last month's theme, which saw 52 new Clojure functions, I have excellent news. We actually beat that this month, adding 56 new Clojure functions! However, I only added 23 of those and the other 33 were added by madstap (Aleksander Madland Stapnes). He did this while also adding the transducer arity into pretty much every existing sequence function. I added volatiles to support him in writing those transducers.


New projects

At this point, I was thinking that jank actually has pretty darn good Clojure parity, both in terms of syntax and essential core functions. So how can I take the best steps toward getting jank onto your computer?

Well, I think the most important thing is for me to start writing some actual projects in jank. Doing this will require improving the tooling and will help identify issues with the existing functionality. The project I've chosen is jank's nREPL server. By the end of the project, we'll not only have more confidence in jank, we'll all be able to connect our editors to running jank programs!

nREPL server

nREPL has some docs on building new servers, so I've taken those as a starting point. However, let's be clear, there are going to be a lot of steps along the way. jank is not currently ready for me to just build this server today and have it all work. I need a goal to work toward, though, and every quest I go on is bringing me one step closer to completing this nREPL server in jank. Let's take a look at some of the things I know I'll need for this.

Module system

jank's module system was implemented two quarters ago, but since there are no real jank projects, it hasn't seen much battle testing. To start with, I will need to work through some issues with this. Already I've found (and fixed) a couple of bugs related to module writing and reading while getting started on the nREPL server. Further improvements will be needed around how modules are cached and timestamped for iterative compilation.

Native interop

Next, jank's native interop support will need to be expanded. I've started on that this month by making it possible to now write C++ sources alongside your jank sources and actually require them from jank! As you may know, jank allows for inline C++ code within the special native/raw form, but by compiling entire C++ files alongside your jank code, it's now much easier to offload certain aspects of your jank programs to C++ without worrying about writing too much C++ as inline jank strings.

jank's native interop support can be further improved by declaratively noting include paths, implicit includes, link paths, and linked libraries as part of the project. This will likely end up necessary for the nREPL server.

AOT compilation

Also required for the nREPL server, I'll need to design and implement jank's AOT compilation system. This will involve compiling all jank sources and C++ sources together and can allow for direct linking, whole-program link time optimizations (LTO), and even static runtimes (no interactivity, but smaller binaries).


Finally, both jank and the nREPL server will need distribution mechanisms for Linux and macOS. For jank, that may mean AppImages or perhaps more integrated binaries. Either way, I want this to be easy for you all to use and I'm following Rust/Cargo as my overall inspiration.

I hope I've succeeded in showing how much work still remains for this nREPL server to be built and shipped out. This will take me several months, I'd estimate. However, I think having this sort of goal in mind is very powerful and I'm excited that jank is far enough along to where I can actually be doing this.

nREPL server progress

Since I have C++ sources working alongside jank source now, I can use boost::asio to spin up an async TCP server. The data sent over the wire for nREPL servers is encoded with bencode, so I started on a jank.data.bencode project and I have the decoding portion of that working. From there, I wanted to write my tests in jank using clojure.test, but I haven't implemented clojure.test yet, so I looked into doing that. It looks like clojure.test will require me to implement multimethods in jank, which don't yet exist. On top of that, I'll need to implement clojure.template, which requires clojure.walk, none of which have been started.

I'll continue on with this depth-first search, implementing as needed, and then unwind all the way back up to making more progress on the nREPL server. Getting clojure.test working will be a huge step toward being able to dogfood more, so I don't want to cut any corners there. Once I can test my decode implementation for bencode, I'll write the encoding (which is easier) and then I'll be back onto implementing the nREPL server functionality.

Hang tight, folks! We've come a long way, and there is still so much work to do, but the wheels are rolling and jank is actually becoming a usable Clojure dialect. Your interest, support, questions, and encouragement are all the inspiration which keeps me going.

Would you like to join in?

  1. Join the community on Slack
  2. Join the design discussions or pick up a ticket on GitHub
  3. Considering becoming a Sponsor
  4. Hire me full-time to work on jank!