VDM-10 Language Manual

VDM-10 Language Manual
✞
✡✝
|| (stmt1, stmt2, ..., stmtn)
✆
and it represents the execution of the component statements stmti in an arbitrary (nondeterministic)
order. However, it should be noted that the component statements are not
executed simultaneously. Notice that the interpreter will use an underdetermined 4 semantics
even though this construct is called a non-deterministic statement.
Examples: Using the VDM-SL state definition
✞
✡✝
state St of
x:nat
y:nat
l:seq1 of nat
end
or the VDM++ instance variables
✞
✡✝
instance variables
x:nat;
y:nat;
l:seq1 of nat;
we can use the non-deterministic statement to effect a bubble sort:
✞
✡✝
Sort: () ==> ()
Sort () ==
while x < y do
||(BubbleMin(), BubbleMax());
✆
✆
✆
Here BubbleMin “bubbles” the minimum value in the subsequence l(x,...,y) to the
head of the subsequence and BubbleMax “bubbles” the maximum value in the subsequence
l(x,...,y) to the last index in the subsequence. BubbleMin works by first iterating
through the subsequence to find the index of the minimum value. The contents of this index
are then swapped with the contents of the head of the list, l(x).
✞
BubbleMin : () ==> ()
BubbleMin () ==
4 Even though the user of the interpreter does not know the order in which these statements are executed they are always
executed in the same order unless the seed option is used.
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