- A loop_statement includes a sequence_of_statements that is to be executed
repeatedly, zero or more times.
end loop [loop_identifier];
iteration_scheme ::= while condition
| for loop_parameter_specification
defining_identifier in [reverse] discrete_subtype_definition
- If a loop_statement has a loop_statement_identifier, then the
identifier shall be repeated after the end loop; otherwise, there shall
not be an identifier after the end loop.
- A loop_parameter_specification declares a loop parameter, which is an
object whose subtype is that defined by the discrete_subtype_definition.
- For the execution of a loop_statement, the sequence_of_statements is
executed repeatedly, zero or more times, until the loop_statement is
complete. The loop_statement is complete when a transfer of control occurs
that transfers control out of the loop, or, in the case of an iteration_scheme, as specified below.
- For the execution of a loop_statement with a while iteration_scheme, the
condition is evaluated before each execution of the sequence_of_statements;
if the value of the condition is True, the sequence_of_statements is
executed; if False, the execution of the loop_statement is complete.
- For the execution of a loop_statement with a for iteration_scheme, the
loop_parameter_specification is first elaborated. This elaboration creates
the loop parameter and elaborates the discrete_subtype_definition. If the
discrete_subtype_definition defines a subtype with a null range, the
execution of the loop_statement is complete. Otherwise, the sequence_of_statements is executed once for each value of the discrete subtype defined by
the discrete_subtype_definition (or until the loop is left as a consequence
of a transfer of control). Prior to each such iteration, the corresponding
value of the discrete subtype is assigned to the loop parameter. These
values are assigned in increasing order unless the reserved word reverse is
present, in which case the values are assigned in decreasing order.
(6) A loop parameter is a constant; it cannot be updated within the sequence_of_statements
of the loop (see 3.3).
(7) An object_declaration should not be given for a loop parameter,
since the loop parameter is automatically declared by the loop_parameter_specification. The scope of a loop parameter extends from the
loop_parameter_specification to the end of the loop_statement, and the
visibility rules are such that a loop parameter is only visible within
the sequence_of_statements of the loop.
(8) The discrete_subtype_definition of a for loop is elaborated just
once. Use of the reserved word reverse does not alter the discrete
subtype defined, so that the following iteration_schemes are not
equivalent; the first has a null range.
for J in reverse 1 .. 0
for J in 0 .. 1
- Example of a loop statement without an iteration scheme:
exit when Current_Character = '*';
- Example of a loop statement with a while iteration scheme:
while Bid(N).Price < Cut_Off.Price loop
N := N + 1;
- Example of a loop statement with a for iteration scheme:
for J in Buffer'Range loop -- works even with a null range
if Buffer(J) /= Space then
- Example of a loop statement with a name:
while Next /= Head loop -- see 3.10.1
Sum := Sum + Next.Value;
Next := Next.Succ;
end loop Summation;
-- Email comments, additions, corrections, gripes, kudos, etc. to:
Magnus Kempe -- Magnus.Kempe@di.epfl.ch
Page last generated: 95-03-12