When Riccardo Terrell hit the concurrency limitations in a jvm application, he thought back to the haskell he learned in a university course and decided to rewrite the entire thing in haskell.  The immutability of the haskell solution made the concurrency bottleneck non-existent.  It is no surprise that years later, his book on concurrency in .net leans heavily on functional programming constructs and the functional features of F# and C#.