Spell casting and paying costs timing

[Tylert]

Let's say I can pay for a card's cost by discarding a card as an alternate casting cost.
Does any "When you cast this spell" trigger see the card in the graveyard??

I'm just trying to figure the exact timing.

[Fox]

If discarding is part of the spell cost, this must be paid to cast a spell. If the spell creates a trigger [at/when/whenever], the discards are in yard already.

[Tylert]

If discarding is part of the spell cost, this must be paid to cast a spell. If the spell creates a trigger [at/when/whenever], the discards are in yard already.

Many thks.

[rufus]

If you want to see the order that stuff happens in while casting spells rule 601 goes over it in painstaking detail.

https://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules