Available here; you will also need the language spec, here.

This implementation is based on a translator for Global Script code embedded in a Haskell source file; to get a working program, you will need to add

import GSI.Env (runGSProgram)
$gsimports

main = runGSProgram $ [gs:value|
    -- Global Script code goes here
|]

around the program, then compile and run that with a Haskell compiler.