Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!willett!ForthNet
From: ForthNet@willett.UUCP (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: UR/FORTH ASSEMBLER
Message-ID: <198.UUL1.3#5129@willett.UUCP>
Date: 5 Jan 90 20:43:53 GMT
Organization: Latest Link in ForthNet Chain
Lines: 26


 Date: 01-02-90 (02:03)              Number: 122
   To: JOHN SOMERVILLE               Refer#: 120
 From: RAY DUNCAN                      Read: NO
 Subj: UR/FORTH ASSEMBLER            Status: PUBLIC MESSAGE

   >Other Forths have eliminated the need for them

 Huh?  All Forths that don't run on stack machines (like the Harris
 RTX2000) are really languages implemented on top of virtual machines
 that are in turn implemented on the real machine.  The virtual machine
 must dedicate several registers in the real machine for its own
 purposes.  These must always be protected in CODE definitions, either by
 not touching them, or by saving and restoring them. 

 If you are telling me that some Forths automatically take care of saving
 and restoring these registers in CODE definitions, then each to his own,
 but I think this is a bad practice.  People who don't understand the
 virtual machine architecture probably shouldn't be writing CODE
 definitions anyway; such automatic protection of registers won't keep
 them out of trouble in other areas, and it will get in the way of
 writing CODE definitions that do *useful* things with the virtual
 machine registers.
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