Date: Wed, 14 Oct 1998 14:24:10 -0400
From: milendor@chicklet.east.sun.com (Michael Milendorf (Godin))
Subject: Item #448: The definition of ABORT" function is unclear

P1275 Open Firmware Working Group Proposal -- Proposal #:448 Ver 1

Title:         Clarification on ABORT" function description

Author:        Michael Milendorf

Date:          October 14, 1998

Ed/Tech:       Technical

Synopsis:      The definition of ABORT" function is unclear

Doc & Version: IEEE Std. 1275-1994

Problem:       IEEE 1275-1994 explains the function of ABORT"
		in the following way: 
              
               If flag is nonzero, display text and call abort.
               Equivalent to: -2 THROW

               The whole description is confusing and unclear. IEEE 1275 refers
               to definition of EXTENSION 9.6.2.0680 ANS Forth ABORT function.
               However the ANS Forth 9.6.2.0680 ABORT function description is 
               not just "-2 THROW" but rather "Remove flag from the stack. If 
               any bit of flag is non-zero, perform the function of -2 THROW, 
               displaying ccc string if there is  no exception frame on the 
               exception stack". This explanation of the function implies that 
               the text may not be displayed in all cases, but only when there
               will be no exception frame on the exception stack,
	       which contradicts
               1275 definition. Therefore we can conclude that the current 1275 
               description of ABORT" function is incorrect, because it says 
               "display text" (in all cases).

               It looks like ANS Forth doesn't specify exactly how EXTENSION 
               9.6.2.0680 ABORT" function may behave. All following behavious 
               are legally fell under the description of 9.6.2.0680 ABORT":

               If there is no exception frame on the exception stack:

               1. Display text first, then execute ABORT.

               2. Execute ABORT first, then the system displays text, because 
                  the system must provide an exception frame on the highest 
                  level to CATCH all possible THROWs.

               If there is an exception frame on the exception stack:

               1. Display text first, then execute ABORT (ABORT is being
                  intercepted half-way through by exception frame).

               2. Execute ABORT first, then ABORT is being intercepted 
                  half-way through by exception frame. At this point the 
                  text may or may not be displayed by the user program. 

               Finally, it is understood that for all ANS Forth words of
               IEEE 1275-1994, the 1275 descriptions may be rather casual
               and usually take a second priority after ANS Forth, when
               clarification is needed. However it would be undesirable
               to alter the meaning or functionality of any specific ANS
               Forth function, like ABORT", by providing too casual 
               definition in IEEE 1275-1994 Std. document.

Proposal:      I would suggest to change the description of ABORT" function of
               IEEE 1275-1994 (p. 107) to the following text:

               The version of ABORT" defined by the ANS Forth EXCEPTION wordset
               applies.

               Another possibility would be to change IEEE 1275 ABORT
	       description to clarify on all possible behavious, as described
	       in the "Problem" section of the current proposal.

[ P1275 Item #448 -- Received: Wed Oct 14 11:24:16 PDT 1998 ]