KOS_OP_MATCH_KEY_VAR / KOS_OP_MATCH_KEY_FAST

• Style: EXTRA (LABEL, VAR) on MATCH_KEY_VAR, (LABEL, FASTVAR) on MATCH_KEY_FAST: label, key.

• Stack: [..., o] -> [..., o, v]; jump to a0 with nothing pushed on a miss.

• Semantics: Push the value under the key in the variable a1, read by name on the _VAR form and by fast index on the _FAST form, in the mapping o read through Datum. An absent key is a miss. The mapping is probed as MATCH_KEY probes it.

• Compiler form: Emitted by the match compiler for a symbol key of a mapping pattern; the _VAR form pre-compile, the _FAST twin once convert_fast has lowered the variable.