Fennel is a lisp that compiles to Lua. It aims to be easy to use, expressive, and has almost zero overhead compared to writing Lua directly.
At https://fennel-lang.org there's a live in-browser repl you can use without installing anything. At https://fennel-lang.org/see you can see what Lua output a given piece of Fennel compiles to, or what the equivalent Fennel for a given piece of Lua would be.
For more examples, see the cookbook on the wiki.
The changelog has a list of user-visible changes for each release.
(print "hello, world!")
(fn fib [n]
(if (< n 2)
n
(+ (fib (- n 1)) (fib (- n 2)))))
(print (fib 10))
Building Fennel from source allows you to use versions of Fennel that haven't been released, and it allows you to contribute to Fennel.
This requires GNU Make and Lua (5.1-5.4 or LuaJIT).
cd
to a directory in which you want to download Fennel, such as ~/src
git clone https://git.sr.ht/~technomancy/fennel
cd fennel
make fennel
to create a standalone script called fennel
sudo make install
to install system-wide (or make install PREFIX=$HOME
if ~/bin
is on your $PATH
)for
Fennel inherits the limitations of the Lua runtime, which does not offer pre-emptive multitasking or OS-level threads. Libraries for Lua work great with Fennel, but the selection of libraries is not as extensive as it is with more popular languages. While LuaJIT has excellent overall performance, purely-functional algorithms will not be as efficient as they would be on a VM with generational garbage collection.
Even for cases where the Lua runtime is a good fit, Fennel might not be a good fit when end-users are expected to write their own code to extend the program, because the available documentation for learning Lua is much more readily-available than it is for Fennel.
#fennel
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The file test/faith.fnl
is copyright © 2009-2023 Scott Vokes, Phil
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