Throw IORs

1. Current Poll Standing
2. Problem
3. Current practice
4. Solution
5. Proposal
6. Comments
7. Voting instructions

Poll standings

Systems

[ ] conforms to ANS Forth.
   PFE (Guido Draheim)
[ ] already implements the proposal in full since release [ ]:
[ ] implements the proposal in full in a development version:
[ ] will implement the proposal in full in release [ ].
[ ] will implement the proposal in full in some future release.
[ ] There are no plans to implement the proposal in full in [ ].
[ ] will never implement the proposal in full:
   PFE

Programmers

[ ] I have used (parts of) this proposal in my programs:
[ ] I would use (parts of) this proposal in my programs if the systems
I am interested in implemented it:
  Graham Smith
[ ] I would use (parts of) this proposal in my programs if this
proposal was in the Forth standard:
[ ] I would not use (parts of) this proposal in my programs.

Problem

  ALLOCATE IF   THROW  ENDIF

: ?THROW    \ ior throwcode --
  SWAP IF  THROW  ELSE  DROP  THEN  ;

  ALLOCATE  ?THROW

  ALLOCATE THROW

Current Practice

Some years ago, some people objected to making iors the same as THROW codes because of the documentation overhead. This RfD is made to sample opinion again, particularly among Forth system implementers.

Solution

Proposal

Labelling

name	Type	Constant?	Meaning
X:ThorwIORs	-	-	the X:ThowIORs extension is present

value	text
-59	ALLOCATE
-60	FREE
-61	RESIZE
-62	CLOSE-FILE
-63	CREATE-FILE
-64	DELETE-FILE
-65	FILE-POSITION
-66	FILE-SIZE
-67	FILE-STATUS
-68	FLUSH-FILE
-69	OPEN-FILE
-70	READ-FILE
-71	READ-LINE
-72	RENAME-FILE
-73	REPOSITION-FILE
-74	RESIZE-FILE
-75	WRITE-FILE
-76	WRITE-LINE

Comments

Bernd Paysan

The ballot system doesn't work well to describe how Gforth and bigFORTH do it, so I explain it in words:

Gforth and bigFORTH have made IORs throwable since the dawn of their ANS Forth compatibility (both during the draft process). However, we use the system-specific part of the throw code table, and have a way how to convert signal and errno numbers into the THROW space.

If you relax your proposal in such a way that IORs must be throwable, and the system also must provide a way to print out diagnostic strings (e.g. the .ERROR we have in Gforth), a consent is easier to reach. I like to keep as much information as possible about the original error, so mapping errors to words that misbehave isn't such a good idea - a word like WRITE-FILE can fail for quite a number of reasons (no space left on device, pipe closed, low-level IO error, buffer outside address space, etc.). A backtracing utility is a better way to locate the error, and you'll then see which word misbehaved, as well.

So in general, I fully support the part of your proposal where IORs are made throwable, but I don't support your throw code scheme.

Stephen Pelc points out that the proposal does not say that you must use these throw numbers, it says that if you use these numbers, this is what the standard means by those specific numbers. Consequently gForth will not conflict with the proposal.

Given the range of hardware and O/S, it is impossible in a standard to go beyond saying that WRITE-FILE failed and a THROW occurred. Most hosted systems require further work to get an extended error code and/or string.

Graham Smith

Yes! And I grow tired of reinventing this sort of thing for each application.

Voting instructions

Note that you can be both a system implementor and a programmer, so you can submit both kinds of ballots.

Ballot for systems

[ ] conforms to ANS Forth.

[ ] already implements the proposal in full since release [ ].

[ ] implements the proposal in full in a development version.

[ ] will implement the proposal in full in release [ ].

[ ] will implement the proposal in full in some future release.

[ ] There are no plans to implement the proposal in full in [ ].

[ ] will never implement the proposal in full.

Ballot for programmers

[ ] I have used (parts of) this proposal in my programs.

[ ] I would use (parts of) this proposal in my programs if the systems I am interested in implemented it.

[ ] I would use (parts of) this proposal in my programs if this proposal was in the Forth standard.

[ ] I would not use (parts of) this proposal in my programs.