In my little Spanish learning experience, I have often read the sentence that uses the term
ir de compras. While I know the meaning of it (go to shopping), I have a trouble in getting the etymology of it.
Why does it uses the form used in second-person singular? For example, we use
Leo un libro antes de dormir., even if the verb is used after
de. We don't write it as
Leo un libro antes de duermes.. But it is not the case in the
ir de compras.
So why does it always use the second-person singular form?