VDM-10 Language Manual

VDM-10 Language Manual
In this example the threadid expression is used in two places:
• In the Wait operation for threads to register interest in this object.
• In the permission predicate for Awake. An interested thread should call Awake following
registration using Wait. It will then be blocked until its threadid is removed
from the waitset following another thread’s call to notify.
Note also that one needs to be careful about the use of the wait-notify mechanism when
having periodic threads (because they change their threadid for each new period).
6.16 The Lambda Expression
Syntax: expression = . . .
| lambda expression
| . . . ;
lambda expression = ‘lambda’, type bind list, ‘&’, expression ;
type bind list = type bind, { ‘,’, type bind } ;
type bind = pattern, ‘:’, type ;
Semantics: A lambda expression is of the form:
✞
lambda pat1 : T1, ..., patn : Tn & e
✡✝
✆
where the pati are patterns, the Ti are type expressions, and e is the body expression.
The scope of the pattern identifiers in the patterns pati is the body expression. A lambda
expression cannot be polymorphic, but apart from that, it corresponds semantically to an
explicit function definition as explained in section 5. A function defined by a lambda expression
can be Curried by using a new lambda expression in the body of it in a nested way.
When lambda expressions are bound to an identifier they can also define a recursive function.
Examples: An increment function can be defined by means of a lambda expression like:
✞
Inc = lambda n : nat & n + 1
✡✝
and an addition function can be Curried by:
✞
Add = lambda a : nat & lambda b : nat & a + b
✡✝
✆
✆
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