coll?

(coll? x)

true for a list, lazy seq, vector, map, set (sorted ones too) or record. nil, the booleans, strings (which the runtime stores as vectors), characters, numbers, keywords, atoms, vars and regex patterns are no collections, like the oracle. nil is the empty list here, so (coll? ()) is false where the oracle answers true. As a value a one-argument lambda answering T-or-false.