VDM-10 Language Manual

Chapter 13. Statements
✡✝
def t = GroupWinner(gp)
in let sct = iota sc in set gps(gp) & sc.team = t
in
let sc in set gps(gp) \ {sct} be st
forall sc’ in set gps(gp) \ {sc,sct} &
(sc.points > sc’.points) or
(sc.points = sc’.points and sc.won > sc’.won)
in
return sc.team
✆
Note the use of the def statement (section 13.2) here; this is used rather than a let statement
since the right-hand side is an operation call, and therefore is not an expression.
13.2 The Define Statement
Syntax: statement = . . .
| def statement
| . . . ;
def statement = ‘def’, equals definition,
{ ‘;’, equals definition },[ ‘;’ ], ‘in’,
statement ;
equals definition = pattern bind, ‘=’, expression ;
Semantics: A define statement has the form:
✞
✡✝
def pb1 = e1;
...
pbn = en
in
s
✆
The define statement corresponds to a define expression except that it is also allowed to use
operation calls on the right-hand sides. Thus, operations that change the state can also be
used here, and if there are more than one definition they are evaluated in the order in which
they are presented. It denotes the evaluation of the statement s in the context in which
the patterns (or binds) pb1, ..., pbn are matched against the values returned by the
corresponding expressions or operation calls e1, ..., en 2 .
2 If binds are used it simply means that the values which can match the pattern are further constrained by the type or set
expression as it is explained in section 7.
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