Mr. T. Janeczko has stated many times about why self referencing Prev is inferior to loop or AMA and about how doing it.
For example, a humbler vector language such as ...err... Zerodha's algoZ offers:
LOOP(Vector1, Vector2, Offset1, Offset2, Operator).
So, to get Fibo's:
Set x = 1;
Set x = LOOP(x, x, 1, 2, ADD);
Do not have algoZ, and not tested, but I imagine that would work. Whether its slow as treacle or has internally been implemented better is an open question.