VDM-10 Language Manual

VDM-10 Language Manual
Examples: The example below, taken from [Fitzgerald&98] assigns token values to identifiers p1
and eid2, an Expert record value to e3 and an Alarm record value to a1.
✞
types
Period = token;
ExpertId = token;
Expert :: expertid : ExpertId
quali : set of Qualification
inv ex == ex.quali {};
Qualification = | | | ;
Alarm :: alarmtext : seq of char
quali : Qualification
values
public p1: Period = mk_token("Monday day");
private eid2 : ExpertId = mk_token(145);
protected e3 : Expert = mk_Expert(eid2, { , });
a1 : Alarm = mk_Alarm("CO2 detected", )
✡✝
✆
As this example shows, a value can depend on other values which are defined previous
to itself. The access modifiers private, protected and public can only be used in
VDM++ and VDM-RT. A top-level VDM-SL specification can consist of specifications from
a number of files or modules (see section 17). It is good practice not to let a value depend on
values defined in other modules as the ordering is important.
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