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Thomas Mayfield

Polyglot programmer who loves the weird beautiful chaos of humans building software together. Fitness nerd. Southern kid living in Massachusetts.

Notes On Writing Clojure In Vim

There a lot of things I like about Clojure as a language, but it requires a lot of tooling setup to not have a bad time. There’s a big chunk of the Clojure community that uses Emacs and the admittedly fantastic CIDER environment, but Vim salwarts who don’t want to ditch years of editor customization aren’t left out in the cold. It took a little more digging and research, but I managed to put together a Vim/Clojure setup with the fast feedback loop that’s so important to productive Clojure dev.

What follows is annotated bits from my .vimrc - you can see the (full source here). I’m using Vundle to manage my plugins.

Plugin 'tpope/vim-classpath'
Plugin 'tpope/vim-fireplace.git'
Plugin 'guns/vim-clojure-static.git'

autocmd Filetype clojure nmap <buffer> gf <Plug>FireplaceDjump

These plugins are the bare minimum you need to get going. They’ll give you syntax highlighting, indentation and a bunch of useful IDE-like tools. To get the most out of these, you’ll want to start a repl session in another window or tab; fireplace will automatically connect to it if present. The shortcuts I use the most:

  • K - show docs for the function under the cursor.
  • gf - go to source for symbol under the cursor. great for zipping around your project or diving down into a libraries source. (remapped above as gf, it’s [C-d by default)
  • cpr - evals the current buffer into the connected repl; if in a clojure.test buffer, runs the tests and prints any failures to the quickfix buffer.
Plugin 'guns/vim-sexp'
Plugin 'tpope/vim-sexp-mappings-for-regular-people'

I think structural editing of s-expressions is one of the underrated perks of working in a lisp. You can a long ways with Vim’s built-in text objects (like ci( for change-inside-parenthesis), but these plugins let you do more advanced stuff like pushing symbols in and out of s-expresions and smartly moving expression boundaries.

Plugin 'guns/vim-slamhound'

autocmd Filetype clojure nnoremap <buffer> <leader>sh :Slamhound<cr>

Slamhound is an editor agnostic tool for managing Clojure namespaces’ require statements—run it on a file and it’ll remove unused imports and add requires for un-imported symbols. I bound it to <leader>sh.

Plugin 'dgrnbrg/vim-redl'
autocmd Filetype clojure imap <buffer> <Up> <Plug>clj_repl_uphist.
autocmd Filetype clojure imap <buffer> <Down> <Plug>clj_repl_downhist.

The Clojure community seems a little hostile to breakpoint debuggers for some reason, but I find them really useful. vim-redl gives you two useful things: a pretty good in-Vim repl (start one in the current file’s namespace with :ReplHere) and actual, factual breakpoint debugging. See the project’s README for the setup, but once included in your lein profile, you can use redl.core/break and redl.core/continue to debug functions run within Vim’s repl session. I rebound <Up> and <Down> in insert mode to page through the command history.

Plugin 'kien/rainbow_parentheses.vim'
let g:rbpt_colorpairs = [
  \ ['blue',        '#FF6000'],
  \ ['cyan',        '#00FFFF'],
  \ ['darkgreen',   '#00FF00'],
  \ ['LightYellow', '#c0c0c0'],
  \ ['blue',        '#FF6000'],
  \ ['cyan',        '#00FFFF'],
  \ ['darkgreen',   '#00FF00'],
  \ ['LightYellow', '#c0c0c0'],
  \ ['blue',        '#FF6000'],
  \ ['cyan',        '#00FFFF'],
  \ ['darkgreen',   '#00FF00'],
  \ ['LightYellow', '#c0c0c0'],
  \ ['blue',        '#FF6000'],
  \ ['cyan',        '#00FFFF'],
  \ ['darkgreen',   '#00FF00'],
  \ ['LightYellow', '#c0c0c0'],
  \ ]
let g:rbpt_max = 16

autocmd BufEnter *.cljs,*.clj,*.cljs.hl RainbowParenthesesActivate
autocmd BufEnter *.cljs,*.clj,*.cljs.hl RainbowParenthesesLoadRound
autocmd BufEnter *.cljs,*.clj,*.cljs.hl RainbowParenthesesLoadSquare
autocmd BufEnter *.cljs,*.clj,*.cljs.hl RainbowParenthesesLoadBraces

Rainbow parentheses give you different colored parens by depth of nesting, which is a nice way to eyeball when you’ve got inbalanced s-expressions. The default colors didn’t play great with my color scheme (jellybeans), so I customized the colors a bit here.

function! IsFireplaceConnected()
    return has_key(fireplace#platform(), 'connection')
  catch /Fireplace: :Connect to a REPL or install classpath.vim/
    return 0 " false

function! NreplStatusLine()
  if IsFireplaceConnected()
    return 'nREPL Connected'
    return 'No nREPL Connection'

function! SetBasicStatusLine()
  set statusline=%f   " path to file
  set statusline+=\   " separator
  set statusline+=%m  " modified flag
  set statusline+=%=  " switch to right side
  set statusline+=%y  " filetype of file

autocmd Filetype clojure call SetBasicStatusLine()
autocmd Filetype clojure set statusline+=\ [%{NreplStatusLine()}]  " REPL connection status
autocmd BufLeave *.cljs,*.clj,*.cljs.hl  call SetBasicStatusLine()

And lastly, I did a little customization of the status line to show whether or not Fireplace was connected to a running Clojure repl. All of the tools above will work without being connected to existing repl process—but because of the JVM’s startup time, running one of their commands cold will freeze Vim while a new process is spun up to eval the code to do whatever you just asked. Running the same command with a warm repl connected is basically instant. I added some functions add either nREPL Connected or No nREPL Connection to the status line so that I remember to start a new repl before I hit K to look up some docs… and grind my teeth while Vim freezes for 10 seconds.

REPL integration

While vim doesn’t have a true integrated REPL-as-subprocess like Emacs’s CIDER does, you can get a pretty nice setup within tmux by binding some keys to send s-expressions to a repl running an adjacent pane. I wrote up my notes on that strategy here.