text: CREATE TABLE cats(name text);
  INSERT INTO cats VALUES ('a'), ('b'), ('c');
  
  CREATE TYPE cat_idx_type AS (name text);
  
  CREATE OR REPLACE FUNCTION cat_idx_func(text) RETURNS cat_idx_type IMMUTABLE STRICT PARALLEL SAFE LANGUAGE sql AS $$
  SELECT ROW($1)::cat_idx_type;
  $$;
  
  CREATE INDEX cats_idx ON cats USING zombodb (cat_idx_func(name)) WITH (url='http://localhost:9200/');
  
  EXPLAIN
  SELECT * FROM cats where cat_idx_func(name) ==> dsl.row_estimate(2,'cat');
  
  DROP TABLE cats;
  DROP TYPE cat_idx_type CASCADE;
  