The Fortress Language Specification - CiteSeerX

treeSum(t : TreeLeaf) = 0
treeSum(t : TreeNode) = do
var accum := 0
do
accum += treeSum(t.left)
also do
accum += treeSum(t.right)
also do
accum += t.datum
end
accum
end
13.13 Label and Exit
Syntax:
Flow ::= label Id Expr + end Id
| exit [Id] [with Expr]
Block expressions may be labeled with an identifier. Syntactically, a label expression begins with the special reserved
word label followed by an identifier, inner expressions (label block), the special reserved word end , and
finally the same identifier. A label expression evaluates its inner expressions in order and any inner exit expression
can exit the label block. Syntactically, an exit expression begins with the special reserved word exit followed
by an optional identifier of the targeted label block with an optional value (exit value), which consists of the special
reserved word with followed by an expression. If an exit expression does not have a with clause, it has an implicit
exit value () . If an exit expression does not exist within a label expression, the value of the label expression
is the value of the last expression of the label block. If an exit expression exists, the expression completes abruptly
and attempts to transfer control to the end of the targeted label block. The targeted label block evaluates to the exit
value of the exit expression. The type of a label expression is a union of the type of the last expression of its label
block and the types of any exit values. The type of an exit expression is BottomType.
If one or more try expressions are nested between an exit expression and the targeted label block, the finally
clauses of these expressions are run in order, from innermost to outermost. Only when every intervening finally
clause has completed normally does the targeted block complete normally. If any finally clause completes abruptly
by throwing an exception, the exit expression fails to exit, the label expression completes abruptly, and the
exception is propagated.
Here is a simple example:
label I 95
if goingTo(Sun)
then exit I 95 with x32B
else x32A
end
end I 95
The expression exit I 95 with x32B completes abruptly and attempts to transfer control to the end of the targeted
label block label I 95 . The targeted label block completes normally with value x32B .
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