failure.rule_unmapped

An attempt block builds a value that can break one of its type's rules, and no arm says which failure that gives.

Area 4, Failures; not declinable; the next step is usually the agent's.

Why Jadpo refuses it

Building a named type from a value known only when the program runs can break the type's rules, such as Quantity's min: 1. When a rule breaks, the caller gets a failure, and the attempt block says which: one arm per rule, or invalid: for every rule without its own. A rule with neither would leave the caller a failure nobody declared, so every rule that can break is mapped.

What it looks like

main.jadpo:

type Count = Int {}type Quantity = Int {    min: 1    max: 1000}type QuantityTooLarge = Failure {    kind: FailureKind.invalid_value}function from_count(n: Count) fails QuantityTooLarge -> Quantity {    var result: Quantity = attempt Quantity(n) {        max: QuantityTooLarge    }    return result}

   |13 |     var result: Quantity = attempt Quantity(n) {   |                            ^^^^^^^^^^^^^^^^^^^^^ can fail at runtime

(agent) at the end of the next: line means your coding agent can make the fix itself.

n is a Count, which has no range, so it can be below 1 as well as above 1000. The block maps only max.

How to fix it

If a count below 1 needs a failure of its own, declare one, add an arm for min, and list the failure after fails:

function from_count(n: Count) fails QuantityTooSmall, QuantityTooLarge -> Quantity {    var result: Quantity = attempt Quantity(n) {        min: QuantityTooSmall        max: QuantityTooLarge    }    ...}

A count below 1 ends from_count with QuantityTooSmall, and one above 1000 with QuantityTooLarge, so the caller can tell them apart.

If one failure will do for every rule, map them all with invalid:, to a failure whose name says so, QuantityOutOfRange here:

function from_count(n: Count) fails QuantityOutOfRange -> Quantity {    var result: Quantity = attempt Quantity(n) {        invalid: QuantityOutOfRange    }    ...}

Any count outside 1 to 1000 ends from_count with QuantityOutOfRange. invalid: can also sit beside other arms: with max: QuantityTooLarge kept, max has its own failure and invalid: covers min.

Related

• Construction failures by rule
• A value built at run time: rule keys and invalid:
• Conditions as proof