VDM-10 Language Manual

VDM-10 Language Manual
Semantics: The function sameclass when applied to object references expression1 and
expression2 yields the boolean value true if and only if the objects denoted by expression1
and expression2 are instances of the same class, and false otherwise.
Examples: Assuming the classes Tree, BinarySearchTree, Queue, and identifiers t, b, q
from section 6.18, and assuming b’ is another instance of BinarySearchTree we have:
sameclass(b,t) ≡ false
sameclass(b,b’) ≡ true
sameclass(q,t) ≡ false
6.22 History Expressions (VDM++ and VDM-RT)
Syntax: expression = . . .
| act expression
| fin expression
| active expression
| req expression
| waiting expression
| . . . ;
act expression = ‘#act’, ‘(’, name, ‘)’
| ‘#act’, ‘(’, name list, ‘)’ ;
fin expression = ‘#fin’, ‘(’, name, ‘)’
| ‘#fin’, ‘(’, name list, ‘)’ ;
active expression = ‘#active’, ‘(’, name, ‘)’
| ‘#active’, ‘(’, name list, ‘)’ ;
req expression = ‘#req’, ‘(’, name, ‘)’
| ‘#req’, ‘(’, name list, ‘)’ ;
waiting expression = ‘#waiting’, ‘(’, name, ‘)’
| ‘#waiting’, ‘(’, name list, ‘)’ ;
Semantics: History expressions can only be used in permission predicates (see section 15.1).
History expressions may contain one or more of the following expressions:
• #act(operation name). The number of times that operation name operation has been
activated.
• #fin(operation name). The number of times that the operation name operation has
been completed.
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