https://github.com/fogus/ulithp

A micro LISP implementation in 24 lines of Ruby.
https://github.com/fogus/ulithp

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A micro LISP implementation in 24 lines of Ruby.

• Host: GitHub
• URL: https://github.com/fogus/ulithp
• Owner: fogus
• License: mit
• Created: 2012-01-25T19:23:59.000Z (almost 13 years ago)
• Default Branch: master
• Last Pushed: 2020-02-13T16:24:16.000Z (almost 5 years ago)
• Last Synced: 2025-01-08T22:26:07.745Z (12 days ago)
• Topics: langdev
• Language: Ruby
• Homepage: http://fogus.github.com/ulithp/
• Size: 49.8 KB
• Stars: 270
• Watchers: 16
• Forks: 33
• Open Issues: 4
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# μLithp

### [Official website and deep analysis](http://fogus.github.com/ulithp)

A micro LISP implementation in 24 lines of Ruby, with a reader in 33 lines, REPL in 35 lines, a compiler in 15 lines and Ruby interop in 13 lines.  Really frickin' small.

* `car`

* `cdr`

* `quote`

* `atom`

* `if`

* `label`

* `cons`

* `eq`

* `lambda`

See the `src/lithp.rb` file for source and `doc/index.org` for implementation details and the original announcement in the  [μLithp blog post](http://blog.fogus.me/2012/01/25/lisp-in-40-lines-of-ruby/).

*this is my entry into the December 2012 [PLT Games](http://www.pltgames.com)*

## Embedded usage

The LISP interpreter is just a Ruby class that evals expressions in Ruby data structures, like so:

```ruby

	 l = Lisp.new

	 l.eval [:label, :a, 42]

	 l.eval :a

	 #=> 42

	 l.eval [:eq, 42, :a]

	 #=> true

	 l.eval [:quote, [1, 2]]

	 #=> [1, 2]

	 l.eval [:car, [:quote, [1, 2]]]

	 #=> 1

	 l.eval [:cdr, [:quote, [1, 2]]]

	 #=> [2]

	 l.eval [:cons, 1, [:quote, [2,3]]]

	 #=> [1, 2, 3]

	 l.eval [:if, [:eq, 1, 2], 42, 43]

	 #=> 43

	 l.eval [:atom, [:quote, [1,2]]]

	 #=> false

	 l.eval [:label, :second, [:quote, [:lambda, [:x], 	 [:car, [:cdr, :x]]]]]

	 l.eval [:second, [:quote, [1, 2, 3]]]

	 #=> 2

```

Have fun!

## REPL usage

In your shell use Ruby 1.9.2 to run the REPL:

```sh

    rvm use ruby-1.9.2

	ruby -I . repl.rb

```

You'll then see a prompt:

    >

Start typing uLithp code:

```lisp

    (car (quote (1 2 3)))

	(cdr (quote (1 2 3)))

	(label third (quote (lambda (x) (car (cdr (cdr x))))))

	(third (quote (1 2 3 4 5)))

```

Enjoy!

## thanks

Thanks to [Russ Olsen](http://eloquentruby.com) for the reader and REPL.

## License

This software is provided as-is under the [MIT license](http://opensource.org/licenses/MIT).