I propose we add pattern guards in comprehensions, but I'm not sure what syntax would work. Consider this function: allMinus :: [Natural] -> [Natural] allMinus m = mapMaybe (-? m) where n -? m | m > n = Nothing | True = Just (n-m) One may wish to write such as a list comprehension, but it is cumbersome: allMinus m ns = [n' | n@((-? m) -> Just n') <- ns] This would be clearer with pattern guards, fictitious syntax here: allMinus m ns = [n' | n <- ns, Just n' <- n -? m] Alas, this conflicts with the other part of list comprehension syntax. Try we this, actual syntax now: allMinus m ns = [n' | n <- ns, let Just n' = n -? m] Nope, that's an error if (any (< m) ns). I recognize in this case the one in terms of mapMaybe is quite clear, but in the case of some other code I'm writing it's much more complicated. Ideas: 1. Modify semantics of let in comprehension to skip that element on pattern mismatch 2. Use another keyword, e.g. [n' | n <- ns where Just n' <- n -? m] Thoughts?