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Functions And Subroutines
5-4
A
statement
function
may
be referenced only in
the
program
unit
where it
is
defined.
The
statement
function
may
not
reference
another
statement
function
if
that
other
function
is
defined later in the
program
unit.
Furthermore,
a
statement
function
in a
FUNCTION
subprogram
must
not
reference
the
name
of
the
subprogram.
A
reference
to
an
external
function
in
the
expression
of
a
statement
function
must
not
cause a
dummy
argument
of
the
statement
function
to
become
undefined
or
redefin-
ed.
5.2 External Procedures
This
section desi:ribes external
procedures,
specifically
procedures
defined by
FUNCTION
and
SUBROUTINE
subprograms.
It
also describes
statements
related
to
external
procedures:
RETURN,
SAVE,
EXTERNAL,
and
the
subroutine
CALL.
5.2.1
FUNCTION Statement
The
FUNCTION
statement
introduces
a
FUNCTION
subprogram.
The
FUNC-
TION
statement
must always be the first
statement
of
the
subprogram
and
the sub-
program
must be
terminated
with
an
END
statement.
The
format
of
the
FUNCTION
statement
is
[typ] FUNCTION tunc
([dum
[,dum]
...
])
where
typ
is
either
INTEGER
[*Ien],
REAL,
or
LOGICAL
[*lenJ, len being
1,2,
or
4.
June
is
the symbolic
name
of
the
subprogram
and
is
an
external
function
name.
dum
is
a
dummy
argument
and
is
either a variable,
array,
or
dummy
procedure
name.
The
FUNCTION
subprogram
name,
appearing
as a variable within the
subprogram,
must
become defined
or
redefined each time the
subprogram
is
executed.
The
value
of
this variable when a
RETURN
or
END
is
executed
is
the value
of
the
function.
An
external
function
in a
subprogram
may use
dummy
arguments
to
return
values in
addition
to the
function
value
returned.
If
'typ'
is
not
specified, the type
and
length
of
'func'
are
determined
by the
default
conventions
described in sections 2.2.2.1
and
2.2.2.2.
5.2.1.1
Referencing External Functions.
An
external
function
is
referenced by specifying its
name
in
an
expression
(along
with all necessary
actual
arguments).
The
actual
arguments
in the reference
must
agree in
order,
number,
type,
and
length
with their
corresponding
dummy
arguments.
One
exception
is
the use
of
a
subroutine
name
as
an
actual
argument;
subroutine
names
do
not
have
an
associated
type.
Actual
arguments
must
also be
one
of
the following:
•
An
expression
•
An
array
name
•
An
intrinsic function
name
•
An
external
procedure
name
• A
dummy
procedure
name
FORTRAN-80