VDM-10 Language Manual

VDM-10 Language Manual
be done with care in complex expressions. Note however that such operation calls are not
allowed to throw exceptions.
With such operation calls the order of evaluation can become important. Therefore the type
checker will allow the user to enable or disable operation calls inside expressions.
The tuple select expression is used to extract a particular component from a tuple. The
meaning of the expression is if e evaluates to some tuple mk (v1,...,vN) and M is an
integer in the range {1,...,N} then e.#M yields vM. If M lies outside {1,...,N} the
expression is undefined.
The function type instantiation is used for instantiating polymorphic functions with the
proper types. It has the form:
✞
✡✝
pf [ t1, ..., tn ]
where pf is the name of a polymorphic function, and t1, ..., tn are types. The resulting
function uses the types t1, ..., tn instead of the variable type names given in the
function definition.
Examples: Recall that GroupA is a sequence (page 54), GroupG is a map (page 55) and selection sort
is a function (page 44):
GroupA(1) ≡ mk Score(,2,0,1,6)
GroupG() ≡ mk (2,1,0)
GroupG().#2 ≡ 1
selection sort([3,2,9,1,3]) ≡ [1,2,3,3,9]
As an example of the use of polymorphic functions and function type instantiation, we use
the example functions from section 5:
✞
≡
let emptyInt = empty_bag[int]
in
plus_bag[int](-1, emptyInt())
✆
✡✝
{ -1 |-> 1 }
✆
6.13 The New Expression (VDM++ and VDM-RT)
Syntax: expression = . . .
| new expression ;
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