Carol & Dave is a minimalist esolang based on Brain-Flak: It replaces the left stack and right stack by Carol's stack that behaves as usual and Dave's queue.
Since Dave is a bit different he interprets 0 as truthy and anything else as
falsy, thus {code} will loop while 0 is the first element in the queue.
Since Carol and Dave are not as used to being the center of attention (unlike Alice & Bob), they constantly fight for it - resulting in a constantly swapping stack/queue.