Actually you're looking for the next() function, right? Which functions exactly as the previous function, but instead returns the value of the next record... Correct?
If so, then the answer is that the next() function does not exist, but there is a way to work around it: sort your data descending (perhaps in a resident table) and use the previous function. This gives the same result.
field1 field2 Next-fieldValue 1 4 5 2 5 NULL
When you load field 1 and 2 from the the table above sorted desc on field 1, the 'next-fieldValue' column can be calculated using the previous(field2) expression.