Radio Shack TRS-80 Owner's Manual page 124

1
TRS-80
MODEL
ill
DISK
SYSTEM
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I
IMIM
CMD"Z"
,
"OFF"
Turns dual video/printer output
off.
DEFFN
Define
Function
owm
function
name
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function
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xdMC
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s!
,
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:
rr.
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-
:
*
v
v H
^-
-
:
'
fiincfiosi
das?.
formula
is
an
sxprsssic-s f.s^s=f«
"iv
!i r*p
"'*
-.
:^k?' v?
;
;^a^
^r.
the
left
side
of
the
equals
sign.
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
deffn
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 (90)
+
9
defines a function to return a
random
value
between
10
and
99.
108