We use Haskell intensively. It is a very useful and easy language. Once you mastered Haskell (and get used to the type system), it feels very natural. It is both usable for scripting and "real" tasks.<p>The trick with Haskell is to model the data you are going to use. Haskell has a good mathematical ground and if you model it right, you can leverage a lot of mathematical tools.<p>We use it on a web project in combination with PostgreSQL. These two match pretty nicely. Both have strong type systems. We wrote an JsonRPC server in haskell, which acts as a secure proxy between the database and the client.<p>We also use it for system scripting. We wrote a special embedded DSL based on arrows for critical tasks. And we use it for the analysis of data. This is mostly a pipeline ala: Parsing -> Interpreting -> Analyzing -> Storing, where every phase has his own data type. It is great for writing parsers.<p>It has the speed of a compiled language and the ease of a scripting language. It doesn't match c or c++ of course in speed. But you can get very close and in almost all cases close enough.<p>The main negative aspect is that it is difficult to reason about your code in terms of performance. And laziness can also do wonderful unexpected things. And bugs in the compiler.