A while ago I was taken unawares by the fact that the operator priority is higher for or than for function application. That is strognly against my functional-programming intuition of application always binding the strongest. Example of the current state:

{ truth =
  set.attribute or function param == (set.attribute or function) param;
}

I'm aware that changing such things is not to be taken lightly – maybe in nix-1.10 it might be bearable? (Unless you actually prefer the current priority.)