The Opa web site says that I cannot: "Firstly, `‘if I'm using AGPL Opa to develop an app does it need to be AGPL, too?’'. Long story short — yes, it does." It would probably be better for me to consult the license, but I don't plan on reading the license just to make sure that I really can't use a language whose developers don't want me to be able to use it