Live development is the way of the future
(With Reviews of Fireplace.vim and LightTable)
Live development is nothing new; it’s been well-explored in Lisps and in other languages like Smalltalk and Erlang since more or less the dawn of man. Emacs was for a long time – and by many still is – considered the only way to develop for Lisp, thanks to SLIME.
But I with projects such as Light Table, and a growing popularity of functional and dynamic languages in general, I think we’ll see live coding become seriously popular as capable mainstream tools collide with capable mainstream languages. After all, there’s so much to be gained.
(Having said that about mainstream tools and languages, fully half of this post deals with using Vim with Clojure, so don’t get too excited.)
What is live development?
Have you ever used a language with a REPL? Python has one when you
python, and Ruby has one with
irb. PHP has a little-used
php -a, and of course every Lisp ever made considers it an essential
When you take a language with a REPL, and use an editor or tool that lets you send the code you’re writing to the REPL and evaluate it, you’re live-developing.
Live development is really excellent for exploratory programming – trying out solutions to problems so you can understand the problem better. This can be anything from writing a small, one-off script to index your MP3 collection, to figuratively flinging code at an undocumented SOAP API to see what you can get to stick. If it’s not a trivial problem, chances are doing some live development can help you understand it better.
Python, JS, and Clojure Live Development with LightTable
It’s easy to use, too; just highlight a line containing a top-level function (JS & Python) or form (Clojure) and press Ctrl+Enter (Cmd+Enter on OSX) to evaluate it. The returned value is displayed right next to the last line, and output to stdout can be viewed in a tucked-away terminal.
Light Table is a really great project, and I’m looking forward to seeing what’s next It’s still in Alpha, and already it’s fantastic for what it’s best at.
An earlier version of this post asserted that virtualenv with python didn’t work,
and that clojure editing outside a leiningen project was not supported. Well, the
man himself found me on Twitter, and it turns
out neither of these were true. The former is solved (on osx) by running
LTCLI=true open -a LightTable, and the latter, well, I don’t know what was
up but it got better when I removed and re-installed LightTable. Maybe
I forgot to eval an (ns) block, that still seems to cause problems.
Clojure Live Development with Vim
I’ve been using Vim as my go-to editor for some years now. Whatever language I write, I use Vim (save Java, because tooling is really Java’s strong point, and because IntelliJ has a competent vim mode).
Clojure is no exception to this. However, when I started using it way back (early 2012), there was no really great way to make use of Clojure’s advanced REPL. I used lein-swank and slimv, but that arrangement broke often and easily, and was buggy at the best of times.
Thankfully, it’s been a whole year and a bit, and now there’s a new kid on the block: Fireplace.vim (Formerly foreplay.vim).
Written by Time Pope of Pathogen fame, Fireplace circumvents the problem of having a crappy repl window by instead providing a more vimmish experience. A quick set of keystrokes, and your code is evaluated and the result displayed in a temporary buffer.
LightTable may have become my tool of choice for Python and JS live editing, but Fireplace provides several killer features that make it (and Clojure by proxy) an exceptionally productive development environment
Fireplace uses nREPL to connect to a running Clojure repl if one is available.
So, you’ll want to open up vim/gvim/mvim to your clojure source file in a lein
project, then run
lein repl to provide a place for that code to run. If no
repl is running and you ask Fireplace to eval your code, it will still do it, but it’ll
have to start up its own repl to do it, so you’re dealing with a JVM spin-up every
time. Once the repl is running, though, evaluating forms is nigh-instant.
Once you open a file with vim, you can use
:%Eval to evaluate the whole thing.
(As is typical for vim instructions, I’ll just be listing the keys you need
Any errors will be reported. You can also select a bunch of lines using
visual selection mode; using
:Eval from there will evaluate just that block.
To evaluate a single form, use
cpp. Between cpp and Eval, I’ve found all my
in-place evaluating needs satisfied.
There are a few ways to access the REPL directly. To open up the Clojure REPL
for a single statement, use
cqp. To open up a small buffer that will be evaluated
as soon as you press Return, use
If you change the
ns form of a file, such as
to add an include, or if you change a dependency, you can use
cpr to Reload
the current file in the repl.
Learning on the go
Besides evaluating, Fireplace.vim provides two small but important features. To
read the documentation for a given function, put your cursor over it and press
K. But, should the documentation fail you, you can press
[d to view the source
of the macro or function your cursor is on, right there in your vim window! This
is an enormously useful feature when working with new and/or less-than-perfectly-documented
This is nothing special to an IDE user, of course, save being way faster and working from vim. But what more do you need?