this might be kind of crude, but I think it does what you want
Code:
alias deal {
  var %cardplayer = $r(1,52)
  cardcheck %cardplayer
}
alias cardcheck {
  var %cardplayer = $1
  if (%cardplayer isin %cardsused) { deal | return }
  if (%cardplayer !isin %cardsused) { set %cardsused %cardsused %cardplayer }
  ;for testing echo to status
  echo card is %cardplayer of %cardsused
  ;whatever other code
}