clojure

# Clojure and Vim: An overview

## It's very possible

Dominic Monroe
Senior Software Engineer

I want to encourage Vim users to continue using Vim as their primary driver, even for Clojure. This isn't about Emacs vs Vim, it is about encouraging people to not change editor because they've changed language.

Vim is a very capable editor. I want to give you an overview of the plugin set I use to work with Clojure every day.

# The core toolset

These are the central parts of my workflow that I build all else from.

## Neovim

At the start of my journey, I switched to Neovim from Vim. Neovim is a fork of Vim that aims to refactor the legacy code base, and bring modern features.

The first innovation from Neovim is async. These have permitted plugins like async-clj-omni to appear for asynchronous auto-completion, and async repl plugins such as acid for non-blocking evaluations.

Another innovation of Neovim's is the fluent RPC api and plugin host capabilities. These allow you to write plugins in any language for vim. In fact, snoe wrote clj-refactor.nvim in Clojurescript, taking advantage of libraries such as rewrite-cljs, for REPL-less refactoring for Clojure.

Writing plugins for a language, in that language, is the way to go

## nREPL middleware

Both CIDER & clj-refactor.el are extremely popular within the Emacs community. Powering both are editor-agnostic APIs available through the nREPL as middleware. This means I get access to much of the same functionality in Vim directly from the same code base.

Due to the accessibility and usefulness of these APIs, they are used in many Clojure plugins. Amongst the many features the middleware provides are:

• Syntax aware completions

• Code refresh (without a dependency)

• An Enhanced doc API including information such as specs

• Locate uses of a var

• Format code

## Fireplace.vim

The fireplace plugin is an nREPL client. It's purpose is to integrate Vim with your REPL. It's a very simple plugin, providing a light interface over the nREPL and common interactions with it. It's the centerpiece of my REPL workflow.

It provides a number of features:

• Evaluation in the buffer cpp

• Command to run arbitary code :Eval (+ 1 1)

• Manual omni-completion you can activate with <C-x><C-o>

• Automatic nREPL connection

• Docs for symbol under cursor K

• Jump to definition [<C-D>

My secret weapon from fireplace is cp. It can evaluate a text object (region of text) you give it. Many overlook the usefulness of this little operation, but it's extremely handy when composed with vim-sexp.

Fireplace takes advantage of CIDER-nREPL for a number of features (e.g. the completion, and augmenting minor functionality), displaying the non-specificity of the middleware.

## Sexp

vim-sexp is the paredit of the Vim world. It would be amiss to not mention vim-sexp-mappings-for-regular-people which adds mappings that are easier to use, but override built-ins.

It has support for a number of operations (slurpage, barfage, raise parent, etc.). It provides text objects which make it easy to refer to sections of code, and there are motions for navigating quickly.

The text objects for referring to parts of s-expressions are an overlooked part of Sexp. I'll use an example where | is my cursor in the snippet:

(def price 500.0)

(defn enterprise-price
[]
(* pr|ice 10))

With ie refers to the "element" I'm on, this is a special meaning in vim-sexp (see the readme for more details on what an element is in sexp). In this case, it refers to price, so combined with fireplace, I can do cpie to evaluate price and see 500.0 printed at the bottom.

ie cpie will evaluate price and print out 10.0 at the bottom of the screen.

af cpaf will evaluate (* price 10) and print out 5000.0 at the bottom of the screen

aF cpaF will re-evaluate the defn and update the function definition

Of course, all these objects are compatible with the operators you already know like yank delete

# 20% improvements

These are some plugins which don't form the backbone of my workflow, but make a 20% improvement.

## Deoplete

Deoplete provides as-you-type asyncronous omnicompletion. Using async-clj-omni you can extend Deoplete's completion to include Clojure. I found the default fireplace completion (combined with auto-completion) would slow down during mass typing and cause the editor to lock up whilst it caught up.

## Custom Bindings

Vim's built-in extensibility means you can very easily add mappings to do things like a reset with ,rs:

nnoremap <localleader>rs :Eval (dev/reset)<CR>

I find that I have a number of minor bindings that are useful for automating repetitive evaluations on a project. They really augment the REPL workflow in their nature.

## Parinfer

parinfer is a great system for editing Lisp code which uses your indentation level to figure out the correct parens to insert. Changing the indentation of your code changes where the parens are placed.

nvim-parinfer.js is a vim plugin written in Clojurescript which adds parinfer support using the original javascript library. It was one of the earliest plugins and is a great way to edit Sexps.

## clj-refactor.nvim

Another plugin by snoe, this plugin adds many of the features from clj-refactor.el to Neovim. Many of the refactorings don't even need a REPL to function. The plugin is, written in Clojurescript, so it can take advantage of the Clojure ecosystem's libraries which have been written to manipulate code. rewrite-cljs, and cljfmt both underly this plugin.

## Acid

Here be dragons, only for the truest of heart.

acid is an upcoming plugin for Neovim that absolutely deserves a mention. It's attempting to rebuild the fireplace you know and love in Python, to add a fully async interface to it. The plugin is in alpha, but is something to keep an eye on.

## neovim-client

neovim-client is a client for Neovim, written in Clojure. The idea is to provide make it simpler to run the JVM clojure as a plugin language for Neovim.

One of the included examples is a socket REPL client, which is a very impressive display of how this library could be used to build plugins for Vim.

## Next Post(s)

Some of my current ideas for future posts:

• A detailed beginner setup guide for all these tools

• Some information on how I have built out my environment, and my favourite mappings

# Me

I share my dotfiles publicly, particularly of interest is probably my clojure folder. Please peruse them, copy from them, learn from them.

You can come bother me in #vim-fireplace as dominicm in the Clojurians Slack, and I'll try my best to help you with Vim.