Editing Vienna Development Method (section)

===Queue abstract data type===
This is a classical example illustrating the use of implicit operation specification in a state-based model of a well-known data structure. The queue is modelled as a sequence composed of elements of a type <code>Qelt</code>. The representation is <code>Qelt</code> is immaterial and so is defined as a token type.
<syntaxhighlight lang="rsl">
 types

 Qelt = token;
 Queue = seq of Qelt;

 state TheQueue of
   q : Queue
 end

 operations

 ENQUEUE(e:Qelt)
 ext wr q:Queue
 post q = q~ ^ [e];

 DEQUEUE()e:Qelt
 ext wr q:Queue
 pre q <> []
 post q~ = [e]^q;

 IS-EMPTY()r:bool
 ext rd q:Queue
 post r <=> (len q = 0)
</syntaxhighlight>