Situation in title, basically.
I think it does work this way, but I haven't seen it come up at all so I wanted to double check to make sure everyone else thinks it works this way.
Basically, I want to know if I activate spell combat and cast haste first, would I get the benefit of the extra attack during the subsequent full attack?
When using Spell Combat you can choose for the spell to take effect before or after your attacks. If you choose "before" then it should give you the extra attack that round. "After" wouldn't start working until the next round.
Think about how you can cast Shocking Grasp during Spell Combat before your attacks and then use Spellstrike to deliver it with an attack during that same full round action.