That code is ultimately compiled to run inside of a register machine. A language may give you a functional interface to something like disk I/O, but the underl

That code is ultimately compiled to run inside of a register machine. A language may give you a functional interface to something like disk I/O, but the underlying implementation is inherently imperative. Or how about the purely functional programming language Elm, whose runtime is imperative JavaScript? For the record, I prefer purely functional programming, but it's not the only tool in the tool box.