KOS_OP_MATCH_DESCEND

• Style: LABEL

• Stack: [..., v] -> [..., cur]; on a miss [..., v] -> [...] and a jump to the label.

• Semantics: The sequence gate on v read through Datum. A pair spine (nil included), a tuple, a list or another sequence type descends, and a cursor over it replaces v; str, bytes, bytearray, a mapping, a set, an iterator and any other value miss. A pair spine is counted once, here: an improper spine is a miss and a spine that loops raises ValueError. Later instructions read a list at its live length and any other sequence at the length it had here.

• Compiler form: Emitted by the match compiler for a sequence pattern and for the subject of a standalone matcher.