[rrobukef]

Not a fan of prolog then? As an excercise, find the guard in this snippet (https://rosettacode.org/wiki/Babbage_problem#Prolog) and imagine such code in a team codebase!

[irjoe]

Quite the opposite :) My preference would be to rely on pattern matching (unification) in the function head:

    def transform_data([_|[]]) do: []

I just wanted an example of using guard clauses. It does depend on the actual code though, there's probably a more elixiry solution.