Some conditions are easy to write in software. If a basket contains three or more items, offer free delivery. Others are much harder. If you want to flag customer messages that sound frustrated, you can search for words like "angry" or "unacceptable", but a customer who writes "I've contacted you three times and I'm still waiting" hasn't used either of them, and anyone reading the message knows exactly how they feel. That second kind of condition is what TypeSafe built Jev fo