mbknor/gt-engine — Issue #1: %{ print 'hello' }%  should work 
Author: mbknor
Created: 2011-12-06 23:08:57+00:00
State: open

There was one issue I encountered though:

%{ print 'hello' }%

prints to output stream in play 1.2.3
and with your new version it seems to print to the standard out.