Function stack 

pub fn stack<O, S>(
    count: usize,
    per: <O as Outputs>::Per,
    write: &(dyn Fn(usize, <O as Outputs>::Cell<'_>, &mut S) -> bool + Sync),
) -> Result<(O, bool), Error>
where
    O: Outputs + 'static,
    S: Default,

Runs write(i, parts, scratch) on each cell i of a stack of count cells, as [each_cell] runs them, and gives the outputs with whether every call said true. parts is cell i’s part of each output k: per[k] items from i * per[k].