VDM-10 Language Manual

Chapter 5
Function Definitions
In the VDM languages we can define first order and higher order functions. A higher order function
is either a Curried function (a function that returns a function as result), or a function that takes
functions as arguments. Furthermore, both first order and higher order functions can be polymorphic.
In VDM++ and VDM-RT functions are automatically available in a static form (i.e. without
having an instance of the defining class). Thus there is no need to use the static keyword that
can be used for operations in VDM++ and VDM-RT. . In general, the syntax for the definition of
a function is:
function definitions = ‘functions’, [ access function definition ],
{ ‘;’ }, access function definition function definition, [ ‘;’ ] ;
access function definition = [ access ], function definition ;
access = ‘public’
| ‘private’
| ‘protected’ ;
function definition = explicit function definition
| implicit function definition
| extended explicit function definition ;
explicit function definition = identifier,
[ type variable list ], ‘:’, function type,
identifier, parameters list, ‘==’,
function body,
[ ‘pre’, expression ],
[ ‘post’, expression ],
[ ‘measure’, name ] ;
implicit function definition = identifier, [ type variable list ],
parameter types, identifier type pair list,
[ ‘pre’, expression ],
‘post’, expression ;
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