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Re: Parser combinator rewrite status

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Not sure what you are trying to accomplish here, but some work was done 
parsing PostScript using Antlr which has some interesting error 
handling. I have just started using Antlr4 myself and at some point will 
probably look at using it to parse PostScript forms.

Jeff Coffield

On 12/06/2020 01:48 AM, luser droog wrote:
> I started redesigning the Parser Combinators following the
> paper by Hutton where he describes adding error reports by
> rewriting everything to operate on a 3-state object. A parser
> can result in an [OK ...] state or it can be [Error ...] or [Fail ...].
> This way you can record some local state at the point that
> an error is discovered and propagate that back down the
> call stack wrapping more local knowledge at each step.
>
> So for the simple tests I've put it to, viz.
>
> 0 0 (abcd\ne) string-input
> (abc) str exec
> report
> pc
>
> 0 0 (abed\ne) string-input
> (abd) str
> (abc) str alt exec
> report
> pc
>
> 0 0 (abed\ne) string-input
> (a)(c) range
> (a)(c) range then
> exec
> report
> pq
>
> That is two success tests and one failure test, I get the following
> (promising) output:
>
> $ gsnd -q -dNOSAFER pc11a.ps
> OK
> [(a) (b) (c)]
> remainder:[[(d) [0 3]] {0 4 (\ne) string-input}]
> stack:
> :stack
> Fail
> [[(after) [(a) []]] [[(after) [(b) []]] [[{(c) eq} (not satisfied)] [[(e) [0 2]] {0 3 (d\ne) string-input}]]]]
> stack:
> :stack
> OK
> [(a) (b)]
> remainder:{0 2 (ed\ne) string-input}
> stack:
> :stack
>
> The "stack:...:stack" parts are just demonstrating that the stacks
> are left nice and clean after each test. And the Failure report has
> the pieces for a nice error message, but it's not quite there yet IMO.
>
> I suppose the next logical step is to try to build a regex engine or
> a tokenizer with it. to be continued...
>

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Parser combinator rewrite status luser droog <luser.droog@gmail.com> - 2020-12-06 01:48 -0800
  Re: Parser combinator rewrite status "Jeffrey H. Coffield" <jeffrey@digitalsynergyinc.com> - 2020-12-07 09:58 -0800
    Re: Parser combinator rewrite status luser droog <luser.droog@gmail.com> - 2020-12-12 01:23 -0800

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