Re: 0 SET-ORDER why?

Krishna Myneni <krishna.myneni@ccreweb.org> writes:

Why is 0 a valid argument to SET-ORDER (from the optional Search-Order
word set)? It can leave a Forth system in a non-recoverable state.

So what?  There are lots of ways to put a Forth system in a
non-recoverable state.

Sentences are separated for emphasis: "If n is zero, empty the search
order."  Why?

Why not?  It's what I would expect from 0 SET-ORDER anyway.

Is your question: "What potential uses does an empty search order
have?" ?

I have seen postings that suggest to use EVALUATE for converting
untrusted input into a number.  There is of course no security
precautions in these postings, but at the very least one could empty
the search order before the EVALUATE and restore it after the EVALUATE
(with the EVALUATE being wrapped with CATCH).  I thought about writing
out the source code, but the main things that would demonstrate is how
inconvenient GET-ORDER and SET-ORDER with their arbitrary number of
stack items are, and how inconvenient the arbitrary number of stack
items produced by EVALUATE is.

Of course, with recognizer sequences, the better way is to use a
recognizer sequence that only contains the number recognizers you
want, no need to mess with the search order.

In kForth (32/64), the sequence
>
0 SET-ORDER
>
leaves the Forth system in a non-recoverable state, and I have to use
Ctrl-C to break out back to the OS shell. This appears to be true in
Gforth as well, although Gforth traps Ctrl-C, so maybe one has to kill
the process from another shell.

In Gforth you can leave the text interpreter in the traditional Unix
way of doing Ctrl-D at the start of a line.

Restoring an empty search order to some more usable default by the
system CATCH handler would be a potential convenience feature, but I
have not experienced an empty search order as a problem yet, and I
don't remember users asking for such a feature, either.  And it would
only catch

0 SET-ORDER

but not the functionally equivalent

WORDLIST 1 SET-ORDER

So why nerf one and not the other?

- anton
--
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
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