I think Scala is a must-learn language IF you plan to use it. If you're on the JVM, and for some reason CAL doesn't work for you then Scala might well be the b

I think Scala is a must-learn language IF you plan to use it. If you're on the JVM, and for some reason CAL doesn't work for you then Scala might well be the best thing available. However, for learning interesting and useful stuff, I'd probably point people more towards Haskell.