VDM-10 Language Manual

Chapter 13. Statements
elseif statement = ‘elseif’, expression, ‘then’, statement ;
cases statement = ‘cases’, expression, ‘:’,
cases statement alternatives,
[ ‘,’, others statement ], ‘end’ ;
cases statement alternatives =
cases statement alternative,
{ ‘,’, cases statement alternative } ;
cases statement alternative = pattern list, ‘->’, statement ;
others statement = ‘others’, ‘->’, statement ;
Semantics: The semantics of the if statement corresponds to the if expression described in section
6.4 except for the alternatives which are statements (and that the else part is optional) 3 .
The semantics for the cases statement corresponds to the cases expression described in section
6.4 except for the alternatives which are statements.
Examples: Assuming functions clear winner and winner by more wins and operation
RandomElement with the following signatures:
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✡✝
clear_winner : set of Score -> bool
winner_by_more_wins : set of Score -> bool
RandomElement : set of Team ==> Team
then the operation GroupWinner if demonstrates the use of a nested if statement (the
iota expression is presented on page 50):
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GroupWinner_if : GroupName ==> Team
GroupWinner_if (gp) ==
if clear_winner(gps(gp))
-- return unique score in gps(gp) which has more points
-- than any other score
then return ((iota sc in set gps(gp) &
forall sc’ in set gps(gp) \ {sc} &
sc.points > sc’.points).team)
elseif winner_by_more_wins(gps(gp))
-- return unique score in gps(gp) with maximal points
-- & has won more than other scores with maximal points
then return ((iota sc in set gps(gp) &
forall sc’ in set gps(gp) \ {sc} &
3 If the else part is omitted semantically it is like using else skip.
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