If the above function mutated 'bar', then it wouldn't be referentially transparent, which is a lot more error prone and problematic than the trivial error your

If the above function mutated 'bar', then it wouldn't be referentially transparent, which is a lot more error prone and problematic than the trivial error your colleague made. That said, that function looks strange. What were those other lines of code doing if they didn't contribute to the result? Doesn't look like a referentially transparent function to me.