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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.

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

Fennel does not contain any telemetry/spyware and never will.

Downloading Fennel

Downloading Fennel on your computer allows you to run Fennel code and compile to Lua. You have a few options for how to install Fennel.

Downloading Fennel with a package manager

Depending on what package manager you use on your system, you may be able to use it to install Fennel. See the wiki for a list of packaging systems which offer Fennel. Packaged versions of Fennel may lag behind the official releases and often only support one version at a time, but they tend to be the most convenient. For instance, if you use Fedora, it should be as easy as running sudo dnf install fennel.

Downloading the fennel script

This method assumes you have Lua 5.1, 5.2, 5.3, 5.4, or LuaJIT installed on your system.

This method requires you to manually update the fennel script when you want to use a newer version that has come out.

  1. Download the fennel script
  2. Run chmod +x fennel-1.5.1 to make it executable
  3. Download and verify the signature (optional).
  4. Move fennel-1.5.1 to a directory on your $PATH, such as /usr/local/bin

Note: You can rename the script to fennel for convenience. Or you can leave the version in the name, which makes it easy to keep many versions of Fennel installed at once.

Downloading a Fennel binary

Downloading a Fennel binary allows you to run Fennel on your computer without having to download Lua, if you are on a supported platform. If you already have Lua installed, it's better to use the script above.

This method requires you to manually update the fennel binary when you want to use a newer version that has come out.

  1. Choose one the options below, depending on your system:
  2. Run chmod +x fennel-1.5.1* to make it executable
  3. Download and verify the signature (optional).
  4. Move the downloaded binary to a directory on your $PATH, such as /usr/local/bin

Embedding Fennel

Fennel code can be embedded inside of applications that support Lua either by including the Fennel compiler inside of the application, or by performing ahead-of-time compilation. Embedding Fennel in a program that doesn't already support Lua is possible but outside the scope of this document.

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, (for instance, if you can only embed one Lua file into the application and it cannot access the disk to load further files) then compiling Fennel code to Lua during the build process and including the Lua output in the application may be easier.

There are so many ways to distribute your code that we can't cover them all here; please see the wiki page on distribution for details.

Embedding the Fennel compiler in a Lua application

The Fennel compiler can be added to your application and then loaded from Lua.

  1. Add fennel.lua to your code repository.
  2. Add the following line to your Lua code:
require("fennel").install().dofile("main.fnl")

Replace main.fnl with whatever filename you use as an entry point. You can pass options to the fennel compiler by passing a table to the install function.

Be sure to use the fennel.lua library and not the file for the entire fennel executable.

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 (AOT) 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; if you use a different build system you can adapt it.

  1. Add the following lines to your Makefile:

    %.lua: %.fnl fennel
	./fennel --compile $< > $@

  2. Ensure your build target depends on the .lua files you need, for example, if every .fnl file has a corresponding .lua file:

    SRC := $(wildcard *.fnl)
OUT := $(patsubst %.fnl,%.lua,$(SRC))
myprogram: $(OUT)
    [...]

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.

Adding Fennel support to your text editor

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.

See the wiki for a list of editors that have Fennel support.

If your editor supports the Language Server Protocol (LSP) then you can install fennel-ls to get highlighting of errors and improved navigation.

Adding readline support to Fennel

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

  • tab-completion on the REPL that can complete on all locals, macros, and special forms
  • a rolling history buffer, which can be navigated, searched (ctrl+r), and optionally persisted to disk so you can search input from previous REPL sessions
  • Emacs (default) or vi key binding emulation via readline's custom support for better line navigation
  • optional use of additional readline features in ~/.inputrc, such as blinking on matched parentheses or color output (described below)

See the wiki page on readline for details of how to install and configure it on your system.

Making games with Fennel

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

TIC-80 is software that acts as a simulated 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. 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 and more difficult to run in the browser.

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 without more complex 3rd-party tools.

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 in its console to get started.

The TIC-80 wiki documents the functions to use and important concepts.

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:

  • Click "start" to begin
  • Press the Esc key and click "Close game"
  • Press Esc again to see the code

Using Fennel with LÖVE

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

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.

You can reference the LÖVE wiki for Lua-specific documentation. Use See Fennel to see how any given Lua snippet would look translated to Fennel.