`separated_fold*1` is a `reduce` operation, not a `fold`

[epage]

separated_foldl1 and separated_foldr1 accept impl FnMut(O, S, O) -> O and return a Result<O>

Iterator::fold accepts (R, impl FnMut(R, O) -> R) and returns an R.

Iterator::reduce accepts FnMut(O, O) -> O and returns an Option<O>.

The parameters better match what Iterator::reduce accept and switching fold for reduce would better align on terminology, making it easier for users to pick up winnow through consistency.

The downside is that the trailing letter looks more odd in this situation. That convention was picked up from chumskey and we may want to consider an alternative

[epage]

naan::Foldable also uses the foldl and foldr names

However, the standard library provides rfold methods.

In that case, the standard library only specializes the name for right-fold and not for left-fold.