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Ballz.js - a small Node.js based LISP interpreter

What is Ballz?

Ballz is a minimal Lisp environment written in Node.js. It was written by Dominik Hübner and Sven Pfleiderer for the Design and implementation of programming languages and virtual machines class at the Media University Stuttgart. Ballz is neither complete nor production ready, but you can install and play with it -- if you are interested.

Installing Ballz

To run Ballz, all you need is a running installation of Node.js (0.4.x). To install Node, have a look at the installation guide in the Node Wiki or run the following commands:

# Download the source package
wget http://nodejs.org/dist/node-v0.4.12.tar.gz
# Extract the sources
tar xvzf node-v0.4.12.tar.gz
cd node-v0.4.12
# Build Node
./configure --prefix=/opt/node
make
make install
# Add Node to your $PATH variable
echo 'export PATH=$PATH:/opt/node/bin' >> ~/.profile

Ballz also depends on the Eyes.js for colored object introspection. For development the Vows testing framework and the Nodelint code quality measurement tool are used.

To install these libraries, you need to install npm:

curl http://npmjs.org/install.sh | sh

After you've installed npm, you can install the dependencies by running the following command inside your Ballz.js directory:

npm install .

Running Ballz REPL

node bin/ballz-repl.js or ./bin/ballz-repl.js

Running Ballz Web-REPL

node bin/ballz-web-repl/ballz-web-repl.js or ./bin/ballz-web-repl/ballz-web-repl.js

Running tests

To run our unit tests, you need to install the development dependencies:

npm install . # in your ballz.js directory

After all dependencies are installed, run make test.

Running lint

To run the jslint/nodelint code quality measurement tool, just run:

make lint

Features

Lang

  • (if (cond) (first-expr) (second-expr)): evaluates first-expr if cond evaluates to true, otherwise evaluates second-expr
  • (quote (expr)): returns expression expr without evluation
  • (eval (expr)): explicitly evaluates expr
  • (define (symbol) (expr)): assigns expr to symbol
  • (lambda (arg-symbols) (body-expr)): creates anonymous function with arguments arg-symbols and function body body-expr
  • (cond ((condition) (expr)) ((condition) (expr)) (else (expr))): evaluates expr if related condition evaluates to true, else is optional if no condition evaluated to true

Pair

  • (cons (expr) (expr)): creates pair of both expressions expr
  • (car (expr)): evaluates to the first value of a pair
  • (cdr (expr)): evaluates to the second value of a pair

Arithmetic

  • (plus (first-expr) (second-expr) … (nth-expr)): evaluates to the sum of all expressions

  • (minus (first-expr) (second-expr) … (nth-expr)): evaluates to the substraction of all expressions

  • (multiply (first-expr) (second-expr) … (nth-expr)): evaluates to the arithmetic product of all expressosions

  • (divide (first-expr) (second-expr) … (nth-expr)): evaluates to the quotient of all expressions

      Both, floating point and integer numbers, may be used.

Logical

  • (and (first-expr) (second-expr) … (nth-expr)): evaluates to the conjuntion of all expressions
  • (or (first-expr) (second-expr) … (nth-expr)): evaluates to the disjunction of all expressions
  • (not (expr)): evaluates to the logical inversion of expr
  • (xor (first-expr) (second-expr)): evaluates to XOR of both expressions

Comparison

  • (equals (expr) (expr)): evaluates to true if both expr evaluate to the same result
  • (greaterthan (expr) (expr)): evaluates to 0 if both expr evaluate to the same result, to 1 if the first expr is greater than the second expr, to -1 if the second expr is greater

Reflection

  • (pair? (expr)): evaluates to true if expr is a pair, otherwise to false
  • (symbol? (expr)): evaluates to true if expr is a symbol, otherwise to false
  • (number? (expr)): evaluates to true if expr is a number, otherwise to false
  • (string? (expr)): evaluates to true if expr is a string, otherwise to false
  • (nil? (expr)): evaluates to true if expr is nil, otherwise to false