Dear all, there is a question I have been thinking about a bit. In short, we could simply formulate it like this: Are there any problems which *cannot *be solved a side effect-free language (such as Haskell)? In other words, are there problems that would explicitly demand semantics that can only be provided by a language allowing direct modification of external state variables, such as Java and C++? If not, are there problems which are simply *infeasible *to solve with a side effect-free language? I realize this question is very broad, and I am not expecting an exact answer by any means. I am asking since I am curious about the relation between functional and imperative/procedural languages in general. I primarily come from a Java background, but I can program Haskell and Erlang, and have recently started exploring Scala, so this would be interesting to know. -- Best, Christopher Svanefalk Student, Department of Computer Science and Engineering University of Gothenburg / Chalmers University of Technology