INSTALL evalexpr_rhai FROM community;
LOAD evalexpr_rhai;

-- Calculate the value of an expression
SELECT evalexpr_rhai('40+2');

┌───────────────────────────────┐
│     evalexpr_rhai('40+2')     │
│ union(ok json, error varchar) │
├───────────────────────────────┤
│ 42                            │
└───────────────────────────────┘

-- Expression's return type is a union of
--
-- ok JSON - the result of the expression as a JSON value
-- error VARCHAR - the error if any from evaluating the expression

-- Demonstrate returning a JSON object from Rhai
SELECT evalexpr_rhai('#{"apple": 5, "price": 3.52}').ok;

┌────────────────────────────────────────────────────┐
│ (evalexpr_rhai('#{"apple": 5, "price": 3.52}')).ok │
│                        json                        │
├────────────────────────────────────────────────────┤
│ {"apple":5,"price":3.52}                           │
└────────────────────────────────────────────────────┘

-- Demonstrate what happens when the expression
-- cannot be parsed, an error is returned.
SELECT evalexpr_rhai('#{"apple: 5}').error;

┌────────────────────────────────────────────────────┐
│       (evalexpr_rhai('#{"apple: 5}')).error        │
│                      varchar                       │
├────────────────────────────────────────────────────┤
│ Open string is not terminated (line 1, position 3) │
└────────────────────────────────────────────────────┘

-- Either .ok or .error will be populated but never both.

-- When evaluating and expression you can also pass in
-- variables via context.
CREATE TABLE employees (name text, state text, zip integer);
INSERT INTO employees values
  ('Jane', 'FL', 33139),
  ('John', 'NJ', 08520);

-- Pass the row from the employees table in as "context.row"
SELECT evalexpr_rhai(
  '
  context.row.name + " is in " + context.row.state
  ',
  {
    row: employees
  }) AS result from employees;

┌───────────────────────────────┐
│            result             │
│ union(ok json, error varchar) │
├───────────────────────────────┤
│ "Jane is in FL"               │
│ "John is in NJ"               │
└───────────────────────────────┘

-- To demonstrate how Rhai can be used to implement
-- a function in DuckDB, the next example creates
-- a macro function that calls a Rhai function
-- to calculate the Collatz sequence length.

CREATE MACRO collatz_series_length(n) AS
  evalexpr_rhai('
    fn collatz_series(n) {
        let count = 0;
        while n > 1 {
          count += 1;
          if n % 2 == 0 {
              n /= 2;
          } else {
              n = n * 3 + 1;
          }
        }
        return count
    }
    collatz_series(context.n)
  ', {'n': n});

-- Use the previously defined macro.
SELECT
  collatz_series_length(range).ok::bigint AS sequence_length,
  range AS starting_value
FROM
  range(10000, 20000)
ORDER BY 1 DESC limit 10;

┌─────────────────┬────────────────┐
│ sequence_length │ starting_value │
│      int64      │     int64      │
├─────────────────┼────────────────┤
│             278 │          17647 │
│             278 │          17673 │
│             275 │          13255 │
│             273 │          19593 │
│             273 │          19883 │
│             270 │          14695 │
│             270 │          15039 │
│             267 │          10971 │
│             265 │          16457 │
│             265 │          16777 │
├─────────────────┴────────────────┤
│ 10 rows                2 columns │
└──────────────────────────────────┘