Option represents either a present value or no value, replacing scattered null checks with a composable container. Its concrete cases are Just(value) and Nothing(). section 5.3
Safely reading a nested value
Instead of checking student, school, and address one by one, map each lookup through an option and provide a fallback: student.map(prop('school')).map(prop('address')).map(prop('country')).getOrElse('Country does not exist!'). section 5.3
Option supports a small set of practical behaviors:
- Maps functions over Just values while leaving Nothing unchanged. section 5.3
- Converts nullable results with fromNullable and supplies defaults with getOrElse. section 5.3
- Keeps absence from throwing until code explicitly attempts to extract a missing value. section 5.3
// safeFindObject :: DB -> String -> Maybe
const safeFindObject = R.curry((db, id) => {
return Maybe.fromNullable(find(db, id));
});
// safeFindStudent :: String -> Maybe(Student)
const safeFindStudent = safeFindObject(DB('student'));
const address = safeFindStudent('444-44-4444').map(R.prop('address'));
address; //-> Just(Address(...)) or Nothing
Follow a database lookup that returns Just(address) or Nothing, then maps a property safely. section 5.3
