basic_loop_statement ::=
 [<< label_name >>] LOOP statement [statement]...
 END LOOP [label_name];

while_loop_statement ::=
 [<< label_name >>] WHILE boolean_expression
 LOOP statement [statement]...
 END LOOP [label_name];

for_loop_statement ::=
 [<< label_name >>] FOR index_name IN
 [REVERSE] lower_bound .. upper_bound
 LOOP statement [statement]...
 END LOOP [label_name];