XO0900: typed hole report

Warning. ??? is a typed hole, valid anywhere an expression is expected. xo check succeeds and reports, for each hole, the expected type, the effects in scope, and in scope values or functions that fit. xo build rejects programs with holes; xo run --holes and xo test --holes allow them and fault if a hole is evaluated. Holes let an agent write a type correct skeleton first and fill it in steps. See core 3.7.

Example

fn retry_after(base: Duration, attempt: Int) -> Duration {
  ???
}

Fix

fn retry_after(base: Duration, attempt: Int) -> Duration {
  base * attempt
}

Run xo explain XO0900 for this text in a terminal, or see section 10.6 of the specification.