Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!mcsun!unido!majestix!uh
From: uh@informatik.uni-kiel.dbp.de (Ulrich Hoffmann)
Newsgroups: comp.lang.forth
Subject: Re: TEXIT
Message-ID: <2236@batman.informatik.uni-kiel.dbp.de>
Date: 13 Feb 91 12:30:53 GMT
References: <9102122127.AA04970@ucbvax.Berkeley.EDU>
Organization: Informatik CAU Kiel BRD
Lines: 51

In <9102122127.AA04970@ucbvax.Berkeley.EDU> wmb@MITCH.ENG.SUN.COM (Mitch Bradley) writes:

B.Rod>> Here's something else which (to my mind) cannot be implemented _efficiently_
B.Rod>> in a portable way using ANS Forth.  Even the inefficient ways are difficult.
B.Rod>>
B.Rod>> : ||   IF R> DROP -1 THEN ;     ( t - t)  ( f - )  ( exit on true)
B.Rod>> : &&   0= IF R> DROP 0 THEN ;   ( t - )  ( f - f)  ( exit on false)

M.Bra>: ||
M.Bra>   POSTPONE DUP  POSTPONE IF  POSTPONE EXIT  POSTPONE THEN
M.Bra>; IMMEDIATE
M.Bra>: &&
M.Bra>   POSTPONE DUP  POSTPONE 0=  POSTPONE IF  POSTPONE EXIT  POSTPONE THEN
M.Bra>; IMMEDIATE

Mitch,
  I think you misinterpreted Brad's words.
  && and || are ment to leave a flag on exit, to _drop_ it otherwise.
  Thus possible definitions might be:

: || ( true -- true&EXIT ) ( false -- )  ( comp: -- )
   POSTPONE DUP  POSTPONE IF  POSTPONE EXIT  POSTPONE THEN  POSTPONE DROP
; IMMEDIATE                                               ( ^^^^^^^^^^^^^ )

: && ( true -- ) ( false -- false&EXIT )  ( comp: -- )
   POSTPONE DUP  POSTPONE 0=  POSTPONE IF  POSTPONE EXIT  POSTPONE THEN  POSTPONE DROP 
; IMMEDIATE                                                            ( ^^^^^^^^^^^^^ )



Apart from that I fully agree to what you stated. 

|| and && CAN implemented portably and (at least runtime efficiently) using ANS Forth.

Ulrich

Ulrich Hoffmann
----------------------------------------------------------------------
Christian-Albrechts-Universitaet Kiel, Institut fuer Informatik
Preusserstr. 1 - 9                   , D - 2300 Kiel 1
Telefon: ++49-431-5604-59            , Telefax: ++49-431-566143
EMail: uh@majestix.informatik.uni-kiel.dbp.de
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Ulrich Hoffmann
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Christian-Albrechts-Universitaet Kiel, Institut fuer Informatik
Preusserstr. 1 - 9                   , D - 2300 Kiel 1
Telefon: ++49-431-5604-59            , Telefax: ++49-431-566143
EMail: uh@majestix.informatik.uni-kiel.dbp.de
----------------------------------------------------------------------