Subject: Bill Wickes article on Alpha & Beta Enter.
Date: 26 Feb 91 18:26:01 GMT
Organization: Oregon State University, CS Dept.
Lines: 40

Author: [William C Wickes]
Subject: HP-48SX Vectored Enter

   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 `ENTER
       (here "`" is the Greek alpha character--character 140).  If present,
       the command line is entered as a string object and `ENTER 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 aENTER
       ("a" is Greek beta--character 223).
       If present, then a string representing the key definition is put on the
       stack, and aENTER 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 `ENTER is to create a more convenient
       binary calculator, where `ENTER slaps a "#" on the front of the command
       line so you don't have to bother when entering numbers.

       William Wickes
       Hewlett-Packard