Simon Rydell
Physics, programming
and the rest

All the ways you can :make it

This is a small summary of a talk I held at Stockholm Vim meetup at Devies May 24 2019. All the code can be found on the corresponding github page.

Running your program from vim

While editing files is usually smooth from vim, how to manage building and running different languages might not be. Here I discuss some different ways of running your program from vim. It is meant to be a explorative journey, so even if you don't like the first example, you might like the second and so on.

Via a terminal

There is nothing wrong with the terminal - so use it! From normal mode you can type :! to make everything thereafter be sent to the underlying shell. For running a python program you could define a neat shortcut as

:nnoremap <leader>r :!python3 <C-R>%<CR>

So that whenever you press <leader>r (by default <leader> is \) vim will send python3 to the underlying shell (assuming you have the file in your open buffer).

If you use tmux, you might like the vimux plugin that will allow you to send commands from one vim instance to a separate tmux pane. This avoid having to wait for the shell command to finish before continuing to edit your file. You also don't have to suspend your current vim instance and drop down to the shell.

How to :make it

:make is the native way of building and running programs from within vim. Whenever the command is invoked, the makeprg variable is checked and then ran as if it were a shell command. By default the makeprg is simply make (check it by typing :echo &makeprg from normal mode). Which is a bit C-centric, but we can of course change it. Keeping with our python example

:set makeprg=python3\ %

This creates a command with equivalent behaviour to the example from before. Only now, you don't have to temporarily suspend your vim instance and the output is piped into the quickfix list. This is a real hint, since what is in the quickfix is usually parsed and tagged text. So how do we parse the output from :make? Vim provides a structured way of doing this through the errorformat variable. It has a whole mountain of options that I won't bore you with (you can check it by typing :echo &errorformat from normal mode). As per usual with things that are difficult and tedious, someone else has probably done it - enter :compiler, a command that sets makeprg and errorformat. The one we want is called pyunit from an old unit test framework (fortunately for us, the output from python hasn't changed much). Set it by typing

:compiler pyunit

This does not however populate makeprg since there are multiple ways of running a python program.

Now you'll see that all errors get caught in a nicely formatted quickfix list that you can navigate between errors with :cnext and :cprevious.

Dispatch the saviour

While :make is great it is still fully synchronous, meaning that your vim instance will freeze until whatever command is in makeprg has finished running.

This is solved with vim-dispatch from the famous tpope. It adds the :Make command which runs makeprg in a whole separate process, freeing your vim instance to do whatever.

So now we can run whichever python script is in our current buffer. But what about when the file is a unit test, or perhaps always need some special parameters? Tpope also built a plugin called vim-projectionist that allows us to define meta data where we can store a file specific makeprg. The meta data is stored in the file .projections.json typically located in your project root directory.

With a project structure as

├── shark
│   ├──
│   └──
└── test

We might have the meta data in .projections.json as

    "shark/*.py": {
        "make": "python3 shark/{}.py"
    "test/test_*.py": {
        "make": "python3 -m unittest test.test_{}"

So that whenever we are working on a unit test, the makeprg is set to run our test suite. This allows you to create very complex structures where everything is just the way you want it.

There is of course not one correct way to run or build a program from vim, I use all of the methods described here. But by exploring multiple of them allows you to choose the best tool for your job and perhaps even forgetting the rest. Remember to sharpen the saw.

Further reading