I use Haskell and C++ primarily. Haskell has local functions, ADTs, hierarchical modules, and good support for streaming and concurrent operations. C++ has (lim

I use Haskell and C++ primarily. Haskell has local functions, ADTs, hierarchical modules, and good support for streaming and concurrent operations. C++ has (limited) local functions and lambdas, classes, nested namespaces, iterators, and...well, let’s not talk about imperative concurrency. These are (mostly) good tools, but I still avoid hierarchy more than one level deep—in my experience it just introduces more complexity than it saves.