VDM-10 Language Manual

Chapter 13. Statements
‘do’, statement ;
set for loop = ‘for’, ‘all’, pattern, ‘in set’, expression,
‘do’, statement ;
index for loop = ‘for’, identifier, ‘=’, expression, ‘to’, expression,
[ ‘by’, expression ], ‘do’, statement ;
Semantics: There are three kinds of for-loop statements. The for-loop using an index is known
from most high-level programming languages. In addition, there are two for-loops for
traversing sets and sequences. These are especially useful if access to all elements from
a set (or sequence) is needed one by one.
An index for-loop statement has the form:
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for id = e1 to e2 by e3 do
s
where id is an identifier, e1 and e2 are integer expressions indicating the lower and upper
bounds for the loop, e3 is an integer expression indicating the step size, and s is a statement
where the identifier id can be used. It denotes the evaluation of the statement s as a sequence
statement where the current context is extended with a binding of id. Thus, the first time
s is evaluated id is bound to the value returned from the evaluation of the lower bound e1
and so forth until the upper bound is reached ie. until s > e2 . Note that e1, e2 and e3
are evaluated before entering the loop.
A set for-loop statement has the form:
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✡✝
for all e in set S do
s
where S is a set expression. The statement s is evaluated in the current environment extended
with a binding of e to subsequent values from the set S.
A sequence for-loop statement has the form:
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✡✝
for e in l do
s
where l is a sequence expression. The statement s is evaluated in the current environment
extended with a binding of e to subsequent values from the sequence l.
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