Kapusta

Kapusta is a Lisp for the Ruby runtime.

It is inspired by Fennel. It is not intended to be production-ready like Clojure: that would be a lot of work, and Ruby is already a rich, elegant language.

Instead, Kapusta aims to bring some of the simplicity and joy of Lisp to Ruby. Where Lua is intentionally minimal, and Fennel follows that design for good reason, Kapusta exists mostly for fun. You can use it for small apps, LeetCode, DragonRuby, or maybe even Rails.

For more information about Kapusta, see the official Fennel documentation and tutorials.

Usage

gem install kapusta
kapfmt --fix examples/fizzbuzz.kap
kapusta examples/fizzbuzz.kap

or

exe/kapusta examples/fizzbuzz.kap

or

exe/kapusta --compile examples/fizzbuzz.kap > examples/fizzbuzz.rb
ruby examples/fizzbuzz.rb

Comparison with Fennel

Kapusta keeps most core Fennel forms. The main differences come from Ruby's runtime and object model.

Fennel	Kapusta
Lua stdlib	Ruby stdlib
:foo is a Lua string	:foo is a Ruby symbol
(. xs 1) is the first element	(. xs 0) is the first element
string.format, table.insert, etc.	use Ruby methods and stdlib instead
values uses Lua multiple returns	values lowers to a Ruby array, usually destructured
with-open, tail!	not provided
macros	not provided for now

Kapusta-specific additions:

• module and class for Ruby host structure, including file-header forms
• ivar (@var) / cvar (@@var) / gvar ($var) escape hatches
• try / catch / finally plus raise for exceptions
• (ruby "...") raw host escape hatch
• a trailing symbol-keyed hash is emitted as Ruby keyword arguments
• a final function literal argument is emitted as a Ruby block

Examples

See examples/.

Formatting

exe/kapfmt

Syntax highlight

For Vim you can use https://git.sr.ht/~m15a/vim-fennel-syntax