Setting up Fennel

This document will guide you through setting up Fennel on your computer. This document assumes you know how to run shell commands and edit configuration files in a UNIX-like environment.

Fennel can be used in non-UNIX environments, but those environments will not be covered in this document.


Downloading and installing Fennel

Downloading and installing Fennel on your system allows you to run Fennel scripts. Currently, you can download and install Fennel using Git or LuaRocks.

Depending on which method you want to use, choose a subsection below:

Tip: If you are using software that supports Fennel, such as TIC-80, you do not need to download Fennel, because you can use it inside of TIC-80.

Using Git to download and install Fennel

Downloading and installing Fennel using Git allows you to use versions of Fennel that haven’t been released yet and makes contributions to Fennel easier.

To download Fennel

  1. cd to a directory in which you want to download Fennel, such as ~/src
  2. Run git clone

To install Fennel

  1. Run cd Fennel
  2. Run make fennel
  3. Copy or link the fennel script to a directory on your $PATH, such as /usr/local/bin

Note 1: Step 2 above will compile Fennel into a standalone script called fennel.

Note 2: If the fennel script exists in one of the directories on your $PATH , you can run fennel filename.fnl to run a Fennel file.

Using LuaRocks to download and install Fennel

LuaRocks contains a repository of Lua software packages. LuaRocks is convenient because it automates the downloading, installation, and uninstallation of Lua software packages.

To download and install Fennel

  1. Ensure the luarocks package is installed on your system
  2. Ensure the ~/.luarocks/bin directory is added to your shell’s $PATH
  3. Run one of

Note: When using luarocks with --local, you’ll need to ensure you have the correct lua path values. You can run eval $(luarocks path --bin) from your shell to set this correctly; see LuaRocks path docs for details.

You can try running fennel --help to confirm the installation succeeded.

Embedding Fennel

Fennel code can be embedded inside of Lua applications by including the Fennel compiler inside of a Lua application, or by performing ahead-of-time compilation.

This section consists of the following subsections:

Note: Embedding the Fennel compiler in an application is the more flexible option, and is recommended. By embedding the Fennel compiler in an application, users can write their own extension scripts in Fennel to interact with the application, and you can reload during development. If the application is more restricted, then compiling Fennel code to Lua during the build process and including the Lua output in the application may be easier.

Embedding the Fennel compiler in a Lua application

The Fennel compiler can be added to your code repository, and then loaded from Lua.

To embed the Fennel compiler in a Lua application

  1. Add fennel.lua to your code repository
  2. Add the following lines to your Lua code:
local fennel = require("fennel")
table.insert(package.loaders or package.searchers, fennel.searcher)
local mylib = require("mylib") -- will compile and load code in mylib.fnl

Note: Optionally, if you want the Fennel REPL to print tables in a more readable format, you can add fennelview.fnl to your code repository. For more helpful compiler errors, you can add fennelfriend.fnl to your code repository.

Performing ahead-of-time compilation

If the target system of your application does not make it easy to add the Fennel compiler but has Lua installed, Fennel offers ahead-of-time compilation. This allows you to compile .fnl files to .lua files before shipping an application.

This section will guide you through updating a Makefile to perform this compilation for you.

To perform ahead-of-time compilation

  1. Add the following lines to your Makefile:
%.lua: %.fnl fennel
    ./fennel --compile $< > $@
  1. Ensure your build target depends on the .lua files you need.

Note 1: Ahead-of-time compilation is also useful if what you are working with requires optimal startup time. “Fennel compiles fast, but not as fast as not having to compile.” – jaawerth

Note 2: It’s recommended you include the fennel script in your repository to get consistent results rather than relying on an arbitrary version of Fennel that is installed on your machine at the time of building.

Expanding your Fennel development experience

You can write Fennel code in any editor, but some editors make it more comfortable than others. Most people find support for syntax highlighting, automatic indentation, and delimiter matching convenient, as working without these features can feel tedious.

Other editors support advanced features like an integrated REPL, live reloading while you edit the program, documentation lookups, and jumping to source definitions.

If your favorite editor isn’t listed here, that’s OK; stick with what you’re most comfortable. You can usually get decent results by telling your editor to treat Fennel files as if they were Clojure or Scheme files.

This section consists of the following subections:

Adding Fennel support to Emacs

Installing fennel-mode gives you syntax highlighting, indentation, paren-matching, a repl, reloading, documentation lookup, and jumping to source definitions.

To add Fennel support to Emacs

See the here for details.

Adding Fennel support to Vim

The fennel.vim plugin offers syntax highlighting and indentation support.

Adding Fennel support to Neovim

Adding Fennel support to Visual Studio Code

Search in the built-in extension manager for “Fennel” to install the vsc-fennel extension. At the time of this writing it only provides syntax support.

Adding readline support to Fennel

The command-line REPL that comes with the fennel works out of the box, but the built-in line-reader is very limited in user experience. Adding GNU Readline support enables such user-friendly features as

Requirements for readline support

All you need to enable readline support is:

The stock Fennel REPL will automatically load and use the readline bindings when it can resolve the readline module, so that’s all you need to get started.

Installing readline.lua

For the official support on getting readline.lua, see the official docs.

The easiest way to get readline.lua is to install it with Luarocks, which will fetch the package and automatically compile the native bindings for you. If you don’t want to use LuaRocks, you can do a manual install.

Installing readline with LuaRocks

# to install globally on the system (requires admin privileges or sudo)
$ luarocks install readline

# to install to the user's local tree
$ luarocks install --local readline

# install for Lua 5.1 (including LuaJIT)
$ luarocks install --lua-version=5.1 readline

Because the readline Lua module contains native bindings to libreadline, be sure it’s installed for the Lua version you intend to use.

Note: If you’ve installed with the --local flag, you may need to ensure your package.path and package.cpath contain its location. See the note on LuaRocks installation for details.

Configuring readline for an enhanced experience

Readline itself has a number of configuration options, which can be set either via the readline.lua API in fennelrc, or in readline’s own ~/.inputrc config file.

Enabling persistent history

To configure the REPL to save the rolling history to file at the end of every session, add the following to your fennelrc with your desired filename:

See the readline.lua documentation for information on its API, most notably other parameters that can be set via rl.set_options.

; persist repl history
(match package.loaded.readline
  rl   (rl.set_options {:histfile  "~/.fennel_history" ; default:"" (don't save)
                        :keeplines 1000}))             ; default:1000

Configuring readline in ~/.inputrc

See the documentation on the readline init file for the full set of options and a sample inputrc.

As of Fennel 0.4.0 and readline.lua 2.6, you can make use of a conditional directive your inputrc for fennel-only configuration options.

The following example adds these behaviors: - Blink on a matching parenthesis when entering ). Useful in a Lisp REPL, where the parens are plentiful! - Enable bracketed paste mode for more reliable pasting from clipboard - When tab-completing on a term with more than one possible match, display all candidates immediately instead of ringing the bell + requiring a second <tab>

# requires Fennel >= 0.4.0 and readline.lua >= 2.6
$if fennel
  set enable-bracketed-paste on
  set blink-matching-paren on
  set show-all-if-ambiguous on

Making games in Fennel

The two main platforms for making games with Fennel are TIC-80 and LÖVE.

TIC-80 is software that acts as a computer in which you can write code, design art, compose music, and lay out maps for games. TIC-80 also makes it easy for you to publish and share the games you make with others. TIC-80 introduces restrictions such as low resolution and limited memory to emulate retro game styles.

LÖVE is a game-making framework for the Lua programming language. Because Fennel compiles to Lua, you can reference the LÖVE wiki when making games with Fennel. LÖVE is more flexible than TIC-80 in that it allows you to import from external resources and use any resolution or memory you like, but at a cost in that it is more complicated to make games in.

Both TIC-80 and LÖVE offer cross-platform support across Windows, Mac, and Linux systems, but TIC-80 games can be played in the browser and LÖVE games cannot.

This section consists of the following subsections:

The Fennel wiki links to many games made in both systems you can study.

Using Fennel in TIC-80

Support for Fennel is built into TIC-80. If you want to use the built-in text editor, you don’t need any other tools, just launch TIC-80 and run new fennel to get started.

All TIC-80 games allow you to view and edit the source and assets. Try loading this Conway’s Life game to see how it’s made:

Using Fennel with LÖVE

LÖVE has no built-in support for Fennel, so you will need to setup support yourself.

This project skeleton for LÖVE shows you how to setup support for Fennel and how to setup a console-based REPL for debugging your game while it runs.

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