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Re: THROW and iors

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Stephen Pelc wrote:
> I posted this around September 2006, but it was not the time. Now
> some people seem to believe it is a good idea that ior return values
> can be THROWn. Here it is again.

No need for bringing this up again.  As far as I can see from the 
current snapshot of Forth200x, this is already in, so you remembering 
that it wasn't a good time is probably wrong :-).  Maybe you got too 
many flames.  We accepted your proposal after some heavy discussions and 
minor modifications in 2007:

http://www.forth200x.org/throw-iors.html

However, I don't know who uses these additional error codes.  We 
certainly use the biased OS error codes, which are also expicitely 
mentioned in Forth200x (and that was the minor modification which made 
me happy).

In Gforth (similar in bigForth) we get

s" /foo" r/w create-file throw 
:1: Permission denied
s" /foo" r/w create-file >>>throw<<<

or this

s" /home/bernd" r/w create-file throw 
:2: Is a directory
s" /home/bernd" r/w create-file >>>throw<<<

And of course, "permission denied" or "is a directory" are outside the 
scope of a Forth standard, these are biased POSIX or Linux or even 
Windows error codes.  And it is of course more useful than VFX Forth, 
where this throw currently still results in a silent abort.

We use a special range of the throw-codes which are fed to strerror() 
(range (-2048,-512]) or strsignal() (range (-512;-256]).  We map some 
error codes (especially from signals) to standard error codes, because 
that way they make more sense (especially a SIGSEGV can mean both an 
address violation as well as stack under/overflow).

To go a bit further into discussion, there are some useful words in the 
error handling which have not yet found a way into the standard draft:

We have .ERROR to display the error, and I think this is insufficiently 
factored, and there should be an ERROR$ (which I just have factored out) 
which converts the number to a meaningful string.  Reference 
implementation might be something like

: error$ ( n -- addr u ) \ human readable error string
    base @ >r decimal
    s>d tuck dabs <# #s rot sign s" error #" holds #> r> base ! ;

Of course, while this is human readable, this still requires looking 
into the manual ;-).  Furthermore, we have EXCEPTION ( addr u -- n ) 
which takes a string and returns an individual (consecutive) throw-code 
(in the system range (-4096,-2048]).  When you pass that n to ERROR$, 
you get your string back.

-- 
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://bernd-paysan.de/

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THROW and iors stephenXXX@mpeforth.com (Stephen Pelc) - 2012-06-23 18:04 +0000
  Re: THROW and iors Bernd Paysan <bernd.paysan@gmx.de> - 2012-06-23 23:17 +0200
    Re: THROW and iors "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-06-24 04:17 -0400
      Re: THROW and iors Coos Haak <chforth@hccnet.nl> - 2012-06-25 22:02 +0200
  Re: THROW and iors anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-06-24 13:01 +0000
  Re: THROW and iors Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-06-25 05:01 -0700
    Re: THROW and iors Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-06-26 01:08 +0000
      Re: THROW and iors jfong <jfong@ms4.hinet.net> - 2012-06-25 20:13 -0700
        Re: THROW and iors BruceMcF <agila61@netscape.net> - 2012-06-26 10:18 -0700
          Re: THROW and iors jfong <jfong@ms4.hinet.net> - 2012-06-26 18:53 -0700
            Re: THROW and iors Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-07-02 21:36 -0700
              Re: THROW and iors anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-03 13:34 +0000
                Re: THROW and iors Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-07-03 21:37 -0700

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