billw@hpcvra.CV.HP.COM (William C Wickes) (03/13/90)
The HP-48SX manuals do not document a very powerful feature that we call
"Vectored ENTER," that allows you in effect to redefine or bypass the
command line parser and to have a shot at the stack etc. after the command
line has been executed.
Keys that execute an automatic ENTER perform a two-step process:
1. The command line is parsed and evaluated.
2. The key definition is executed.
When flags -62 and -63 are both set, the system extends this process as
follows:
1. The current path is searched for a global variable named *aENTER
(here "*a" is the Greek alpha character--character 140). If present,
the command line is entered as a string object and *aENTER is
executed. If absent, the command line is parsed and evaluated
normally.
2. The key definition is executed.
3. The current path is searched for a global variable named *bENTER
("*b" is Greek beta--character 223).
If present, then a string representing the key definition is put on the
stack, and *bENTER is executed. The string is the key definition
object's name if it is a command, XLIB name, global or local name, or
an empty string for other object types; its primary purpose is to implement
things like the TRACE mode on other calcs, where you can print a running
record of what you do.
A simple example of the use of *aENTER is to create a more convenient
binary calculator, where *aENTER slaps a "#" on the front of the command
line so you don't have to bother when entering numbers.