VDM-10 Language Manual

Chapter 13. Statements
✞
✡✝
ResetStack();
...
top := PopStack();
✆
where PopStack could be defined as:
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✡✝
PopStack: () ==> Elem
PopStack() ==
def res = hd stack in
(stack := tl stack;
return res)
pre stack []
post stack˜ = [RESULT] ˆ stack
✆
where stack is a global variable.
In VDM++ and VDM-RT this Stack example can be made like:
✞
class Stack
instance variables
stack: seq of Elem := [];
operations
public Reset: () ==> ()
Reset() ==
stack := [];
public Pop: () ==> Elem
Pop() ==
def res = hd stack in
(stack := tl stack;
return res)
pre stack []
post stack˜ = [RESULT] ˆ stack
✡✝
end Stack
✆
In the example the operation Reset does not have any parameters and does not return a
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