Radio Shack TRS-80 model III Owner's Manual page 107

TRS-80
MODEL
III
DISK
SYSTEM
Turns dual
video/printer output
off.
DEFFN
Define
Function
formula
function
does.
formula
is
an
expression
usually involving the
argument(s)
|
the
teM^
The def fn statement
lets
you
create
your
own
function.
That
is,
you
only
have
to call
the
new
function
by name, and
the associated operations will
automatically
be performed.
Once
a function
has
been defined with the
def fn
statement,
you can
call
it
simply
by
inserting
fn
in front
of function
name.
You
can use
it
exactly as
you might
use
one of the built-in
functions, like sin,
abs,
and strings.
The type of variable
used
for
function
name
determines the
type of value the
function will return.
For example,
if
function
name
is
single precision,
then that
function
will
return a single-precision value, regardless of the precision of the
arguments.
The
particular variables
you use
as
arguments
in the
def fn statement
(argument-1,
.
.
.)
are
not assigned to the
function.
When
you
call
the
function
later,
any
variable
name
of
the
same
type
can be
used.
Furthermore, using a variable as
an
argument
in
a
def fn statement has
no
effect
on
the
value of that variable.
So you can use that particular
variable in
another
part
of
your
program
without worrying about interference
from def
fn.
The
function
can be
defined with
no arguments
at
all, if
none
are required.
For example:
DEF FNR
=
RND
(9(3) + 9
defines a
function
to
return
a
random
value
between
10
and
99.
106