VDM-10 Language Manual

VDM-10 Language Manual
Semantics: The self expression has the form:
✞
self
✡✝
✆
The self expression returns a reference to the object currently being executed. It can be used
to simplify the name space in chains of inheritance.
Examples: Using the class Tree defined on page 28 we can specify a subclass called BST which
stores data using the binary search tree approach. We can then specify an operation which
performs a binary search tree insertion:
✞
Insert : int ==> ()
Insert (x) ==
(dcl curr_node : Tree := self;
✡✝
while not curr_node.isEmpty() do
if curr_node.rootval() < x
then curr_node := curr_node.rightBranch()
else curr_node := curr_node.leftBranch();
curr_node.addRoot(x);
)
✆
This operation uses a self expression to find the root at which to being traversal prior to
insertion. Further examples are given in section 13.9.
6.15 The Threadid Expression (VDM++ and VDM-RT)
Syntax: expression = . . .
| threadid expression ;
threadid expression = ‘threadid’ ;
Semantics: The threadid expression has the form:
✞
threadid
✡✝
✆
The threadid expression returns a natural number which uniquely identifies the thread in
which the expression is executed. Note that periodic threads gets a new threadid at the start
of each new period.
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