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General Formats (Cont.) [ Micro Focus COBOL Language Reference ] MPE/iX 5.0 Documentation

Micro Focus COBOL Language Reference

General Formats (Cont.)

The PERFORM Statement (Cont.)

General Rules.

All Formats.

1. When procedure-name-1 is specified, the PERFORM statement is
referred to as an out-of-line PERFORM statement;

For ANS85 only: when procedure-name-1 is omitted, the PERFORM
statement is referred to as an in-line PERFORM statement.

2. The statements contained within the range of procedure-name-1
(through procedure-name-2 if specified) for an out-of-line PERFORM
statement

For ANS85 only: or contained in the PERFORM statement itself for
an in-line PERFORM statement

are referred to as the specified set of statements.

3. For ANS85 only: The END-PERFORM phrase delimits the scope of the
in-line PERFORM statement. (See the section Explicit And Implicit
Scope Terminators in the chapter Concepts of the COBOL Language.).

4. For ANS85 only: An in-line PERFORM statement functions according
to the following general rules for an otherwise identical
out-of-line PERFORM statement, with the exception that the
statements contained within the in-line PERFORM statement are
executed in place of the statements contained within the range of
procedure-name-1 (through procedure-name-2 if specified). Unless
specifically qualified by the word in-line or out-of-line, all the
general rules which apply to the out-of-line PERFORM statement
also apply to the in-line PERFORM statement.

5. When the PERFORM statement is executed, control is transferred to
the first statement of the specified set of statements (except as
indicated in General Rules 8b, 8c and 8d). This transfer of
control occurs only once for each execution of a PERFORM
statement. For those cases where a transfer of control to the
specified set of statements does take place, an implicit transfer
of control to the end of the PERFORM statement is established as
follows:

a. If procedure-name-1 is a paragraph-name and
procedure-name-2 is not specified, the return is after the
last statement of procedure-name-1.

b. If procedure-name-1 is a section-name and procedure-name-2
is not specified, the return is after the last statement of
the last paragraph in procedure-name-1.

c. If procedure-name-2 is specified and it is a
paragraph-name, the return is after the last statement of
the paragraph.

d. If procedure-name-2 is specified and it is a section-name,
the return is after the last statement of the last
paragraph in the section.

e. For ANS85 only: If an in-line PERFORM statement is
specified, an execution of the PERFORM statement is
completed after the last statement contained within it has
been executed.

f. For MF only: An EXIT PERFORM statement can be used to
exit an in-line perform before executing all statements
within the in-line perform.

6. There is no necessary relationship between procedure-name-1 and
procedure-name-2 except that a consecutive sequence of
operations is to be executed beginning at the procedure named
procedure-name-1 and ending with the execution of the procedure
named procedure-name-2. In particular, GO and PERFORM
statements can occur between procedure-name-1 and the end of
procedure-name-2. If there are two or more logical paths to the
return point, then procedure-name-2 can be the name of a paragraph
consisting of the EXIT statement, to which all of these paths must
lead.

7. If control passes to the specified set of statements by means
other than a PERFORM statement, control will pass through the last
statement of the set to the next executable statement as if no
PERFORM statement referenced the set.

8. The PERFORM statements operate as follows:

a. Format 1 is the basic PERFORM statement. The specified set
of statements referenced by this type of PERFORM statement
is executed once and then control passes to the end of the
PERFORM statement.

b. Format 2 is the PERFORM...TIMES. The specified set of
statements is performed the number of times specified by
integer-1 or by the initial value of the data item
referenced by identifier-1 for that execution. If at the
time of the execution of a PERFORM statement, the value of
the data item referenced by identifier-1 is equal to zero
or is negative, control passes to the end of the PERFORM
statement. Following the execution of the specified set of
statements the specified number of times, control is
transferred to the end of the PERFORM statement.

During execution of the PERFORM statement, reference to
identifier-1 cannot alter the number of times the specified
set of statements is to be executed from that which was
indicated by the initial value of the data item referenced
by identifier-1.

Interger-1 must be zero or positive, but it may be signed.

c. Format 3 is the PERFORM...UNTIL. The specified set of
statements is performed until the condition specified by
the UNTIL phrase is true. When the condition is true,
control is transferred to the end of the PERFORM statement.
If the condition is true when the PERFORM statement is
entered, and the TEST BEFORE phrase is specified or
implied, (ANS85 only) no transfer to procedure-name-1 takes
place, and control is passed to the end of the PERFORM
statement.

If the TEST AFTER phrase is specified, the PERFORM
statement functions as if the TEST BEFORE phrase were
specified except that the condition is tested after the
specified set of statements has been executed. Any
subscripting or reference modification associated with the
operands specified in condition-1 is evaluated each time
the condition is tested (ANS85).

For MF only: When UNTIL EXIT is specified, the specified
set of statements is performed repeatedly until some
statement in the set causes this repetition to end. In the
case of an out-of-line PERFORM, the only statements that
will cause this termination are statements such as EXIT
PROGRAM and STOP RUN. In the case of an in-line PERFORM,
the repetition can also be terminated by the EXIT PERFORM
statement and the GO TO statement.

d. Format 4 is the PERFORM...VARYING. This variation of the
PERFORM statement is used to augment the values referenced
by one or more identifiers or index-names in an orderly
fashion during the execution of a PERFORM statement. In
the following discussion, every reference to identifier as
the object of the VARYING, AFTER, and FROM (current value)
phrases also refers to index-names.

If index-name-1 is specified, the value of identifier-3,
index-name- 2, or literal-1 at the beginning of the
execution of the PERFORM statement must correspond to an
occurrence number of an element in the table associated
with index-name-1. If index-name-3 is specified, the value
of identifier-6, index-name-4, or literal-3 at the
beginning of the execution of the PERFORM statement must
correspond to an occurrence number of an element in the
table associated with index-name-3.

Subsequent augmentation, as described below, of
index-name-1 or index-name-3 must not result in the
associated index being set to a value outside the range of
the table associated with index-name-1 or index-name-3;
except that, at the completion of the PERFORM statement,
the index associated with index-name-1 can contain a value
that is outside the range of the associated table by one
increment or decrement value.

If identifier-2 or identifier-5 is subscripted, the
subscripts are evaluated each time the content of the data
item referenced by the identifier is set or augmented. If
identifier-3, identifier-4, identifier-6, or identifier-7
is subscripted, the subscripts are evaluated each time the
content of the data item referenced by the identifier is
used in a setting or augmenting operation. Any
subscripting or reference modification associated with the
operands specified in condition-1 or condition-2
is evaluated each time the condition is tested.
Representations of the actions of several types of Format 4
PERFORM statements are given on the following pages.

i. If the TEST BEFORE phrase is specified or implied:

When the data item referenced by one identifier is
varied, the content of the data item referenced by
identifier-2 is set to literal-1 or the current
value of the data item referenced by identifier-3 at
the point of initial execution of the PERFORM
statement; then, if the condition of the UNTIL
phrase is false, the specified set of statements is
executed once. The value of the data item
referenced by identifier-2 is augmented by the
specified increment or decrement value (literal-2 or
the value of the data item referenced by
identifier-4) and condition-1 is evaluated again.
The cycle continues until this condition is true, at
which point control is transferred to the end of the
PERFORM statement. If condition-1 is true at the
beginning of execution of the PERFORM statement,
control is transferred to the end of the PERFORM
statement.

Figure 4-1: The VARYING Option of a PERFORM Statement with the TEST BEFORE Phrase Having One Condition

After the contents of the data items referenced by
the identifiers have been set, condition-1 is
evaluated; if true, control is transferred to the
end of the PERFORM statement; if false, condition-2
is evaluated. If condition-2 is false, the
specified set of statements is executed once, then
the content of the data item referenced by
identifier-5 is augmented by literal-4 or the
content of the data item referenced by identifier-7
and condition-2 is evaluated again.

This cycle of evaluation and augmentation continues
until this condition is true. When condition-2 is
true, the content of the data item referenced by
identifier-2 is augmented by literal-2 or the
content of the data item referenced by identifier-4,
the content of the data item referenced by
identifier-5 is set to literal-3 or the current
value of the data item referenced by identifier-6,
and condition-1 is reevaluated. The PERFORM
statement is completed if condition-1 is true; if
not, the cycle continues until condition-1 is true.

Figure 4-2: The VARYING Option of a PERFORM Statement with the TEST BEFORE Phrase Having Two Conditions

At the termination of the PERFORM statement, the
data item referenced by identifier-5 contains
literal-3 or the current value of the data item
referenced by identifier-6. The data item
referenced by identifier-2 contains a value that
exceeds the last used setting by one increment or
decrement value, unless condition-1 was true when
the PERFORM statement was entered, in which case the
data item referenced by identifier-2 contains
literal-1 or the current value of the data item
referenced by identifier-3.

ii. For ANS85 only: If the TEST AFTER phrase is
specified:

When the data item referenced by one identifier is
varied, the content of the data item referenced by
identifier-2 is set to literal-1 or the current
value of the data item referenced by identifier-3 at
the point of execution of the PERFORM statement;
then the specified set of statements is executed
once and condition-1 of the UNTIL phrase is tested.
If the condition is false, the value of the data
item referenced by identifier-2 is augmented by the
specified increment or decrement value (literal-2 or
the value of the data item referenced by
identifier-4) and the specified set of statements is
executed again. The cycle continues until
condition-1 is tested and found to be true, at which
point control is transferred to the end of the
PERFORM statement.

Figure 4-3: The VARYING Option of a PERFORM Statement with the TEST AFTER Phrase Having One Condition

When the data items referenced by two identifiers
are varied, the content of the data item referenced
by identifier-2 is set to literal-1 or the current
value of the data item referenced by identifier-3;
then the current value of the data item referenced
by identifier-5 is set to literal-3 or the current
value of the data item referenced by identifier-6;
and the specified set of statements is then
executed. Condition-2 is then evaluated; if false,
the content of the data item referenced by
identifier-5 is augmented by literal-4 or the
content of the data item referenced by identifier-7
and the specified set of statements is again
executed. The cycle continues until condition-2 is
again evaluated and found to be true, at which time
condition-1 is evaluated. If false, the content of
the data item referenced by identifier-2 is
augmented by literal-2 or the content of data item
referenced by identifier-4, the content of the data
item referenced by identifier-5 is set to literal-3
or the current value of the data item referenced by
identifier-6 and the specified set of statements is
again executed. This cycle continues until
condition-1 is again evaluated and found to be true,
at which time control is transferred to the end of
the PERFORM statement.

After completion of the PERFORM statement, each data
item varied by an AFTER or VARYING phrase contains
the same value it contained at the end of the most
recent execution of the specified set of statements.
See Figure 3-4.

Figure 4-4: The VARYING Option of a PERFORM Statement with a TEST AFTER Phrase Having Two Conditions

During the execution of the specified set of
statements associated with the PERFORM statement,
any change to the VARYING variable (the data item
referenced by identifier-2 and index-name-1), the BY
variable (the data item referenced by identifier-4),
the AFTER variable (the data item referenced by
identifier-5 and index-name-3), or the FROM variable
(the data item referenced by identifier-3 and
index-name-2) will be taken into consideration and
will affect the operation of the PERFORM statement.

When the data items referenced by two identifiers
are varied, the data item referenced by identifier-5
goes through a complete cycle (FROM, BY, UNTIL) each
time the content of the data item referenced by
identifier-2 is varied. When the contents of three
or more data items referenced by identifiers are
varied, the mechanism is the same as for two
identifiers except that the data item being varied
by each AFTER phrase goes through a complete cycle
each time the data item being varied by the
preceding AFTER phrase is augmented.

9. The range of a PERFORM statement consists logically of all those
statements that are executed as a result of executing the PERFORM
statement through execution of the explicit transfer of control to
the end of the PERFORM statement. The range includes all
statements that are executed as the result of a transfer of
control by CALL, EXIT, GO TO and PERFORM statements in the range
of the PERFORM statement, as well as all statements in declarative
procedures that are executed as a result of the execution of
statements in the range of the PERFORM statement. The statements
in the range of a PERFORM statement need not appear consecutively
in the source program.

10. Statements executed as the result of a transfer of control caused
by executing an EXIT PROGRAM statement are not considered to be
part of the range of the PERFORM statement when:

a. the EXIT PROGRAM statement is specified in the same program
in which the PERFORM statement is specified, and

b. the EXIT PROGRAM statement is within the range of the
PERFORM statement.

11. If the range of a PERFORM statement includes another PERFORM
statement, the sequence of procedures associated with the included
PERFORM should itself either be totally included in, or totally
excluded from, the logical sequence referred to by the first
PERFORM. Thus, an active PERFORM statement, whose execution point
begins within the range of another active PERFORM statement should
not allow control to pass to the exit of the other active PERFORM
statement; furthermore, two or more such active PERFORM statements
should not have a common exit.

For MF only: These restrictions are not enforced. PERFORM
statements can be freely nested, and recursion (a PERFORM
statement performing a procedure containing it) is allowed. Only
the exit point of the innermost PERFORM statement currently being
executed is recognized. These rules can be changed by use of the
PERFORM-TYPE directive (see your COBOL System Reference).

See the following illustrations for examples of legal PERFORM
constructs.

12. A PERFORM statement that appears in a section that is not in an
independent segment can have within its range, in addition to any
declarative sections whose execution is caused within that range,
one of the following:

a. Sections and/or paragraphs wholly contained in one or more
non-independent segments.

b. Sections and/or paragraphs wholly contained in a single
independent segment.

For OSVS and VSC2 only: These restrictions do not apply.

13. A PERFORM statement that appears in an independent segment can
have within its range, in addition to any declarative sections
whose execution is caused within that range, only one of the
following:

a. Sections and/or paragraphs wholly contained in one or more
non-independent segments.

b. Sections and/or paragraphs wholly contained in the same
independent segment as that PERFORM statement.

For OSVS and VSC2 only: These restrictions do not apply.

Format 4.

14. The data items referenced by identifier-4 and identifier-7 must
not have a zero value.

15. If an index-name is specified in the VARYING or AFTER phrase, and
an identifier is specified in the associated FROM phrase, the
data item referenced by the identifier must have a positive
value.

MPE/iX 5.0 Documentation