Haskell is one of my favorite languages and just wrote a book using Haskell (you can read it free online: https://leanpub.com/haskell-cookbook )

That said there are a lot of tasks that I use Ruby for (text wrangling), Python (machine learning), and Java (huge number of useful libraries).

I use Haskell for NLP, some web apps, and coding algorithms that don't require libraries that aren't available for Haskell. If Haskell had a huge set of 3rd party libraries like Java, then I would probably use it for most of my development.