To shuffle a deck of cards, you might be inclined to go the classic TI-BASIC route and write some complicated co-sorting algorithm, but you don't need to! The Fisher-Yates Shuffle algorithm is way easier and faster. An example implementation in TI-BASIC to shuffle L1 looks like:

dim(L1→N
For(K,N,2,-1
randInt(1,K→A
L1(K→B
L1(A→L1(K
B→L1(A
End

In Grammer, it is just about as easy. You need to first initialize your deck with something like:

.Assume Z points to the deck of 52 cards (52 bytes)

For K,0,51
WriteB(Z+K,K
End

Then every time you want to shuffle, just call (assuming Z still points to the deck):

.SHUFFLE
51→K
While K>0
randInt(0,K→A
(Z+K→B
WriteB(Z+K,(Z+A
WriteB(Z+A,B
K-1→K
End
End