AllThatIsWrongWithImperativeCode

Imperative.scala

// result is never used, can this line be removed?
val result = calculate(input)

update(input)

save(input.child)

foo()

// can the above four lines be re-arranged in a different order? 
// can foo even be deleted?

I do not know how scala works... So I will assume 'input' could be affected by the calculate method.
Then update depends on input, and might also change the child portion of input.
since input.child could have been changed in the above lines, save is required here.
foo() seems arbitrary.

I would be reluctant to change the order. Why bother? What would it gain? You'd be an idiot to unilaterally change that code with no tests or no understanding of the code's inner workings.

That you are required to know what calculate, update, save and foo do internally to be able to reason about this snippet of code is the point here. Such a thing would not be required in e.g.: Haskell.