# optionresult.ludic — the safety value types: `option` (some/none, "maybe a
# value") and `result` (ok/err/try, "a value or a failure"). Each assertion that
# holds prints its number, so a full run prints:
#   1 2 3 4 5 6 7 8 9 10 11 12
# option is issue #53; result shipped in #46. Both are additive — a program that
# does not use them compiles byte-identically.
program OptionResult {
  # a lookup that may find nothing — no magic -1 sentinel
  function slot_of(id: int) -> option {
    if id < 0 { return none() }
    return some(id * 10)
  }
  # a fallible parse — a value or a message
  function to_digit(c: int) -> result {
    if c >= '0' and c <= '9' { return ok(c - 48) }   # '0'..'9'
    return err("not a digit")
  }
  entry {
    # --- option ---
    let a = some(42)
    if is_some(a) { print(1) }
    if not is_none(a) { print(2) }
    if unwrap_or(a, -1) == 42 { print(3) }
    let b = none()
    if is_none(b) { print(4) }
    if unwrap_or(b, -1) == -1 { print(5) }
    if unwrap_or(slot_of(5), 0) == 50 { print(6) }
    if is_none(slot_of(-1)) { print(7) }

    # --- result + try/else ---
    if is_ok(to_digit(55)) { print(8) }
    if is_err(to_digit(120)) { print(9) }
    let d = try to_digit(55) else { 0 }        # '7' -> 7
    if d == 7 { print(10) }
    let bad = try to_digit(120) else { -1 }  # not a digit -> fallback
    if bad == -1 { print(11) }
    let msg = try to_digit(120) else { print(12);  0 }   # else binds `error`
  }
}