Recognizing Horn clauses

Question

I am currently studying model theory and I am trying to decide if a clause is a Horn Clause. I know that a Horn Clause is a clause with at most one positive literal, but there are some clauses that it is not easy to decide whether they are Horn or not.

E.g.,

(P->Q)->W

Is there any way to decide whether this clause is Horn or not, or do I have to make further calculations in order to bring it to a Disjunction form?