It appears to use Scheme syntax for packages. Not ideal in my opinion but I guess it beats shell scripts (since you have full access to a real programming language).
Originally Posted by Cyber Killer
This example was in the slides:
(uri (string-append "mirror://gnu/.../hello-" version ".tar.gz"))
(sha256 (base32 "0wqd...dz6"))))
(synopsis "Hello, GNU world: An example GNU package")
(description "Produce a friendly greeting.")