212
P
P
R
R
O
O
G
G
R
R
A
A
M
M
M
M
I
I
N
N
G
G
T
T
H
H
E
E
H
H
P
P
3
3
9
9
G
G
+
+
T
T
h
h
e
e
d
d
e
e
s
s
i
i
g
g
n
n
p
p
r
r
o
o
c
c
e
e
s
s
s
s
An overview
Although you can choose to simply create programs which are self sufficient
the whole point of working on the hp 39g+ is to use aplets. Hence this
chapter will concentrate on the process of creating aplets with enhanced
powers provided by attached ‘helper’ programs.
The key to the entire process of creating completely new aplets is the
VIEWS
menu and its controlling command function
SETVIEWS
. This function allows
you to override the normal behavior of an aplet and superimpose new
properties by linking in a set of programs written by you.
It is mildly deceptive to call these aplets “new”, as they derive from one of the
standard ones, but the modification of the
VIEWS
menu means that their final
appearance and behavior can be very different to the aplet they derive from.
Essentially the process involves the following stages…
•
Choose the parent aplet;
•
Analyze the expected behavior and design the
VIEWS
menu;
•
Write the ‘helper’ programs and attach them to the aplet using the
SETVIEWS
function;
•
Add supporting documentation.
Choosing the parent aplet
The first stage in the creation process is to decide which of the standard
aplets you wish to make the “parent” of your new child aplet. For some
aplets this may not matter, but for others this can be a very important choice.
All the abilities of the parent are inherited by the child so the parent choice is
crucial if your aplet requires particular abilities. The most commonly used
parent aplets are the Function and Statistics aplets, whereas the Quadratic
and Trig Explorers would probably not make good parent aplets, since they
are specialized teaching aplets without the flexibility of the others.
