i was going to mention this, but the comment was already long :) of course, this doesn't stop you from implementing it as stackPop _ = Nothing or just doing

i was going to mention this, but the comment was already long :) of course, this doesn't stop you from implementing it as stackPop _ = Nothing or just doing the wrong thing. but it does prevent you from returning `([1,2,3], Nothing)`, and that's always one less thing to worry about - if not for the implementer, then for the users. and the more the signature constrains possible implementations¹, the better! and this might be subjective, but for me `Maybe (Stack a, a)` results in less cognitive load. with `(Stack a, Maybe a)` if i do case stackPop xs of (_, Nothing) -> ... (xs2, Just x) -> ... in the back of my head i'm going to be thinking "hmm, am i 100% sure i can throw away that first value if i get a Nothing in there? if it's useless, why does the function return it?²" whereas with case stackPop xs of Nothing -> ... Just (xs2, x) -> ... i know for certain there's no new values introduced in Nothing case – great, less things to keep in my head! it's a small thing to be sure, but i like when the types assist me like this :) --- ¹ parametricity is one of my favorite things in pure FP! ² but i hate throwing things away, so it might just be that...