nil is just an atom, specialcased by the parser to be able to leave off the colon.
In my opinion having marker or value is deemed to fail anyway. What if is I want to insert exactly the value you use as marker?
Please use a tagged tuple or at least provide an API similar to Map get/fetch/fetch! to be able to differentiate when necessary.
Also when you say, it’s collectable and enumerable, in which direction? Is there a way to collect/enumerate in the opposite direction?
Oh I haven’t noticed that Yaq is not a wrapper around :queue, that’s interesting. Speaking of efficiency, do you plan to do some benchmarks? Would be nice to see how it performs compared to :queue.
I’ve had this same though about using atoms as markers. It’s a pretty common pattern in Erlang/OTP from what I can see, but the scenario you describe seems likely, especially when using common atoms like :ok (or nil).
I liked your suggestion about following the get/fetch/fetch! paradigm in Map and elsewhere, so I added a couple functions to the API:
fetch/1 and fetch_r/1 will return the tuple {value, updated_queue} if there are elements on the front or back of the queue, respectively, or :error otherwisefetch!/1 and fetch_r!/1 will return the tuple {value, updated_queue} if there are elements on the front or back of the queue, respectively, or raise Yaq.EmptyQueueError otherwiseI also added a default value specification for dequeue/2 and dequeue_r/2 to follow the pattern from get.
You can only enumerate and collect from front to back, but you can reverse the queue in constant time with Yak.reverse/1, so I think it is a fair compromise.