To download and build rainbow:

  git clone git://github.com/conanite/rainbow.git
  cd rainbow
  ant jar
  cd src/arc

Open a REPL

  java -server -jar rainbow.jar

Open welder.arc in welder:

  java -server -jar rainbow.jar -e '(welder "src/arc/rainbow/welder.arc")'

Play tetris:

  java -server -jar rainbow.jar -e '(tetris)' 

Command-line options:
  --strict-arc              # don't include anarki-compatible extensions
  -f file1 ... fileN        # evaluate each file
  -e '(arc axpr)'           # evaluate arc expr (after having evaluated -f, if specified)
  -args a b c               # sets "*argv*" in the arc environment to (a b c). This option, if present, must be 
  specified last.