That's an interesting question. Does extending a protocol somehow slow down the data structure at all? What do you want (pop []) to return? nil? Are you suggesting the change be made to the cljs core or are you asking if this is a good idea in general? I think in the later case then my gut is that i would want (pop []) to return nil to. I feel like it just allows for slightly more concise code in some cases because you can use if-let and when-let (when-let [x (pop s)] (...)) as opposed to (when (seq s) (let [x (pop s) ...))

> I think in the later case then my gut is that i would want (pop []) to return nil to. I feel like it just allows for slightly more concise code in some cases because you can use if-let and when-let There are some tradeoffs here. I believe clojure has chosen difference tradeoffs and I would implement core protocols such as peek and pop to be consistent with the clojure core data structures. See https://clojure.org/reference/lazy#_the_victim_nil_punning. I don't see anything wrong with your implementation of peek and pop using first and rest since that's essentially how List is implemented (see https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L3113). I'm not that familiar with IndexedSeq and Cons, but I think your example looks ok. Just note that first might not be the right option for peek depending on the data structure (See https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L672).

I think popping [] gonna throw just to keep backward compatibility. But popping nil is a precedent that there are cases where it does not blow up, and therefore it is sort of ok for any empty collection not to blow up on pop. My question is both "am I not considering some unintended consequences by extending these coll types?" and "was it just overlooked in cljs.core, or there is an actual reason those don't implement stack".

> first might not be the right option that's right. The snippet is just an illustration.

if you're building an app, extending core types is probably fine. make sure you don't do it in a library though!

tbh I've only ever used peek/pop on a queue

what’s the best way to check whether every character in a string is a digit?

“12764” “236235" etc