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> doing anything practical with languages like Erlang or Haskell Why do learn it for a specific reason? Why not learn a language to expand your mind? Scala is awesome, but Haskell will help you make use of some of its more powerful features. By all means, learn both. Erlang is interesting and is quite practical too (albeit Scala tends to be practical in more kinds of problems: there many times where you want an easie…
I don't have an opinion about erlang or scala, but I agree with the poster that it is important to do something practical with a language. How will you learn the concepts that a language tries to teach you without actually building something non-trivial in it?
There's tons of practical applications built in both Haskell and Erlang: erlang has rabbit mq (I have some criticisms of it, but they're not related to the language it's built in), Haskell has XMonad (the window manager I use on a daily basis). Both are very practical.