I don't write here often, but I also work on open source projects.

The final language of 7 Languages in 7 Weeks was Haskell, the only pure functional language in the book. This is the only chapter where I completely gave up on most of the exercises. More on that later...

Oooooo.... Clojure. Along with Scala, this was one of my most anticipated languages (mainly because of the JVM integration). Clojure is a dialect of Lisp, which is a very old family of programming languages. Most of the syntax is just parentheses.

Chapter 5 of 7 Languages in 7 Weeks is on Erlang. Erlang is a functional language with a strong focus on concurrency and reliability. Its syntax is based on Prolog (i.e. it's weird). The author described it as a language that "makes easy things hard, and hard things easy".

Just crossed the halfway point of 7 Languages in 7 Weeks with Scala. This is a hybrid object-oriented and functional language. It's a JVM based language, and provides interoperability with existing Java code. Like, Java it has strong static typing. Unlike Java, Scala can infer types in many cases, removing a lot of extra typing. For example in Java:

Next up in 7 Languages in 7 Weeks was Prolog. This is a logic programming language. Your "code" defines facts and rules, and then executes queries on them. It's all declarative, you don't ever see the algorithm that Prolog uses. It's a very different way of thinking, since you are just describing the problem, and asking Prolog to solve it for you.