Error model

Norm distinguishes failure values within a normal contract from Exceptions that interrupt normal evaluation.

Result

std.core.Result<T, E = String> is an ordinary generic enum defined by the standard library. An application domain uses it to return mutually exclusive outcomes explicitly through a function contract. A switch handles it explicitly; the language has no hidden automatic-propagation operator.

Both Ok and Err carry a String msg whose default is the empty string. A simple failure uses Result<T> and Result.Err("message"), with String as the default error type. For programmatic classification, use Result<T, Failure> and Result.Err(Failure.Invalid, msg: "message"). msg supplies information for users or boundaries; it does not replace an explicit error type.

String message = switch reserve(command: command) {
    case Ok(Reservation value) { break value.id }
    case Err(_, String msg) { break msg }
}

Result<String> simple = Result.Err("Name is required")
Result<String, ReservationFailure> typed =
    Result.Err(ReservationFailure.Unavailable, msg: "No seats remain")

Ordinary absence

Use a nullable return type when a lookup misses and error details are unnecessary. The application domain decides whether Result belongs in a contract; it cannot bypass the system-level exception boundary.

Exception

std.core.Exception is the nominal class root of all throwable exceptions. Exception subclasses use ordinary single inheritance. A catch accepts only a non-nullable, non-generic Exception subtype. throw, try, catch, and finally handle exceptions that cannot continue as the current function's normal result. Norm has no checked exceptions and does not automatically turn Result.Err into an Exception.

Failures in the current system-facing I/O, filesystem, HTTP, and time operations all throw domain Exceptions instead of returning Result. See the standard-library overview for the delivered scope.

Toolchain faults such as runtime argument errors, out-of-bounds access, and division by zero use stable runtime error codes. They are outside the user Exception hierarchy and cannot be intercepted by catch.

Boundary conversion

A transport layer may map a domain Result to an HTTP status, and a CLI may map it to an exit code. Mapping occurs in boundary functions, keeping core business types independent of transport protocols.

A return, throw, break, or continue produced by finally replaces the original completion. Libraries should use scoped-resource APIs where possible to reduce ambiguity from cleanup failures.