The license or terms-of-use seem weird: "Picat can be used for any fair purpose, including commercial applications. The C source code is available to registered developers and users free of charge. The project is open to anybody and you are welcome to join, as a developer, a sponsor, a user, or a reviewer. Please contact firstname.lastname@example.org"
Why make things complicated with these conditions? If you are going to allow source access, why not use a standard open source license. If you aren't, if you want to control of the language for some purpose, make it clear this is a commercial product.
The GPL (and other standard open source licenses) are a real commercial licenses at this point. Roll-your-own software licenses seem a lot like roll-your-own device device drivers - might have made sense in yesterday's world but not today.
The Picat C-source code is distributed under the Mozilla Public License (http://mozilla.org/MPL/2.0/). You are assumed to agree to the terms and conditions as described in the license if you submit this request. Please provide a valid email address.
I would wonder if Picat has similar feature (to implicit backtracking in imperative loops)?
Loops in Picat are compiled to recursive calls. And there is automatic backtracking, like in Prolog.