μLithp
Official website and deep analysis
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.
this is my entry into the December 2012 PLT Games
Embedded usage
The LISP interpreter is just a Ruby class that evals expressions in Ruby data structures, like so:
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:
rvm use ruby-1.9.2
ruby -I . repl.rb
You'll then see a prompt:
>
Start typing uLithp code:
(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 for the reader and REPL.
License
This software is provided as-is under the MIT license.