On escape hatches: being able to do imperative style processing is great. A loop-and-mutation is often a much more readable way to write what could be written a

On escape hatches: being able to do imperative style processing is great. A loop-and-mutation is often a much more readable way to write what could be written as a fold or (worse) some tail recursive method. F# does this very well I think, with imperative code sitting quite naturally inside an ML dialect. More importantly, it allows describing the how (or at least something more closer resembling the how) of the computation rather than just describing what is being calculated.