lazy-seq

(lazy-seq body...)

Answers a lazy seq: the body (an implicit do) runs the first time the seq is realized -- through first/rest/next/seq/take/drop/map/filter/concat -- at most once per seq object, and its answer is the seq's contents. Realization is per element, so infinite seqs terminate behind take; a body that never gets taken never runs. There is no chunking: every element realizes singly. The body is its own zero-arity recur target: a recur in tail position re-runs the thunk itself (a recur with arguments is an arity error). A body answering another lazy seq is forced in a loop, like the oracle, so a body that skips by answering the next lazy-seq runs in constant stack however long the run.

Printing realizes a lazy seq, like the oracle: an empty one prints (), and an infinite one prints without end, so print an infinite seq behind take.