Given that Foldable currently has: - foldr and foldr' - foldl and foldl' - foldMap and foldMap' and also has only: - foldr1 - foldl1 it seems natural to ask whether there it should also have a strict variant of at least foldl1, since the non-strict variant has rather limited applicability, and users would/should in most cases want/use the strict `foldl1'` instead. -- Viktor. P.S. I just joined the list today, but noticed that coincidentally, there's already a recent dicussion of Foldable1, which rather overlaps with this question, and perhaps the partial `foldr1` and `foldl1` should be seen as deprecated, once a suitable class of non-empty containers provides total variants. But perhaps on the other hand, given that the partial functions already exist, perhaps adding the strict companions is warranted? I am asking because I am writing some expository prose for Data.Foldable, to go at the bottom of the document, structurally along the lines of what I contributed for Data.Traversable, but with a fairly different focus. The goal is draw careful distinctions between strict recursive and lazy corecursive reductions, explaining their proper usage and typical implementations. The "missing" `foldl1'` was something I ran into while working on part of the writeup.