The Fortress Language Specification - CiteSeerX

Chapter 14
Exceptions
Exceptions are values that can be thrown and caught, via throw expressions (described in Section 13.25) and catch
clauses of try expressions (described in Section 13.26). When a throw expression “throw e ” is evaluated, the
subexpression e is evaluated to an exception. The static type of e must be a subtype of Exception. Then the throw
expression tries to transfer control to its dynamically containing block (described in Chapter 4), from the innermost
outward, until either (i) an enclosing try expression is reached, with a catch clause matching a type of the thrown
exception, or (ii) the outermost dynamically containing block is reached.
If a matching catch clause is reached, the right-hand side of the first matching subclause is evaluated. If no matching
catch clause is found before the outermost dynamically containing block is reached, the outermost dynamically
containing block completes abruptly whose cause is the thrown exception.
If an enclosing try expression of a throw expression includes a finally clause, and the try expression completes
abruptly, the finally clause is evaluated before control is transferred to the dynamically containing block.
14.1 Causes of Exceptions
Every exception is thrown for one of the following reasons:
1. A throw expression is evaluated.
2. An implementation resource is exceeded (e.g., an attempt is made to allocate beyond the set of available locations).
14.2 Types of Exceptions
All exceptions have type Exception declared as follows:
trait Exception comprises { CheckedException, UncheckedException }
settable message: MaybeString
settable chain: MaybeException
printStackTrace():()
end
Every exception has either type CheckedException or UncheckedException:
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