Parse, Don't Validate

Do not merely check data and then throw the proof away. Parse it into a type that carries the proof.

Workflow

1. Find validators that return bool, void, or throw while leaving the original untyped value in circulation.

2. Define a target type whose construction proves the invariant.

3. Replace validation calls with parser or smart-constructor calls that return Result, Either, option, or exceptions as appropriate for the language.

4. Change downstream APIs to accept the parsed type.

5. Remove redundant re-validation.

Checks

• A parsed type should make invalid states unrepresentable.