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³ GOTO ³  by Joseph K. Horn, permanently brain damaged by BASIC.
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So you want to jump into the middle of a System RPL routine, but the
Laws of RPL told you that it's impossible?  It can be done!

System RPL has a GOTO in it!  HP's documentation didn't explain how it
works, but it's simple:

    GOTO (foo), where (foo) is a five-nibble address (NOT a system
    binary!) jumps immediately to address (foo), where RPL continues.

This allows us to jump smack into the middle of any operating system
RPL program!  However, (foo) must NOT be a program prolog.  There are
supported means for jumping to supported objects.  GOTO is intended
ONLY for jumping into the *middle* of objects.

Don't worry; it can't result in spaghetti code, because it only works
on fixed addresses, so you can't use it to jump around within the
running program itself.

There are also two conditional versions: ?GOTO jumps if TRUE is on
level one; NOT?GOTO jumps if FALSE is on the stack.  Both remove the
flag before jumping.  Neither returns; it's not a GOSUB.  These occur
in the HP 48 operating system more than 200 times, so don't worry that
it isn't the way HP would write software...

The magic addresses:

619CB  GOTO      jump to subsequent 5-nibble absolute address
619E0  ?GOTO     if TRUE then DROP GOTO else DROP
619F3  NOT?GOTO  if FALSE then DROP GOTO else DROP

-jkh-   EQU   akcs.joehorn@hpcvbbs.cv.hp.com