Dominion: If a second supply pile is emptied while I am discarding for the Poacher, will I need to discard another card?

Question

Suppose that I have a single empty supply pile. If I play Poacher, I will have to discard a card from my hand. If I discard a Tunnel, I can reveal it to gain a gold.

Question: If I do so and thereby empty the gold pile, will I need to discard another card for the Poacher?

When is the number of empty supply piles evaluated? Only once before I start discarding, or again after each discarding?

Answer 1

You do the effects in order:

1. +1 card
2. +1 action
3. +1 coin
4. Discard a card per empty supply pile.

When you get to #4, you find that there's one empty supply pile, so you discard one card. The "Discard N Cards" effect means you discard all N cards all at once, not in sequence.

From the wiki:

If you discard multiple cards at once, you do not need to allow others to see all of them, just the one you put on top.

So in this case, discarding that one Tunnel will allow you to empty another supply pile, but you don't redo step 4.