dash.el has long been a staple in the Emacs community and I give it a lot of credit for driving some upstream API progress. By showing how many people wanted to use dash.el for various reasons (e.g. macros like -if-let and -when-let and numerous functions that transform sequences), a strong case could be made with Emacs’s maintainers that core Emacs Lisp APIs needed to be extended. Eventually that lead to the creation of subr-x.el1 (bundled with Emacs since 24.3) and seq.el (bundled with Emacs since 26.1). The two packages mostly obsolete dash.el and I guess this contributed to it being used less and less these days.

I recently took over the maintenance of the popular Flycheck package and I’ve noticed that it was still using dash.el, despite targeting Emacs 26.1. As I plan to submit Flycheck to the official NonGNU ELPA package repository, it couldn’t have dependencies that are not present on GNU ELPA and NonGNU ELPA and I needed to remove dash.el. Doing so turned out to be trivial, as there were obvious built-in alternatives for everything Flycheck was using:

  • I replaced -if-let(*) and -when-let(*) with if-let(*) and when-let(*) from subr-x.el.
  • I replaced -any? and -first with seq-find, -all? with seq-every-p and -take with seq-take.

And that was it! The whole process literally took me 10 minutes, most of them spent checking whether seq-find is the right replacement for -any? and -first.

One small caveat to keep in mind, when depending on the built-in Emacs packages like seq.el, is that you should typically stick to whatever version of the package was bundled with the version of Emacs that you target (in my case Emacs 26.1 bundles seq.el 2.20), otherwise you’ll need to declare an explicit package dependency on the newer version. Keep in mind, however, this might cause some issues in packages that are depending on your package, but not declaring the same dependencies.2 Transitive dependencies in Emacs are a messy topic…

So, all it all it was a very quick and easy process and I can totally recommend to other packages that are still relying only on basic dash.el functionality to replace it as well. Now Flycheck is totally dependency-free and it’s ready for submission to NonGNU ELPA!

  1. Originally authored by yours truly. ↩

  2. See https://github.com/flycheck/flycheck/issues/2054. ↩