-- 3-arg wr: serialise a value as JSON and write it in one call.
-- Equivalent to `wr path (jdmp data)`, but type-checks data of any shape.
dump>R t t;wr "/tmp/ilo_wr_json_example.json" (mset (mset mmap "x" 1) "y" 2) "json"
-- run: dump
-- out: /tmp/ilo_wr_json_example.json