- From: M Joel Dubinko <micah@dubinko.info>
- Date: Sat, 17 Sep 2022 23:56:48 -0400
- To: public-ixml@w3.org
Taking through a technical issue for an audience of fellow implementers.
Others may find this thread exceedingly dull. :)
Hopefully writing this out should be enough for me to figure out the
problem. (But if you're reading this, that means I hit 'Send' and thus
could benefit from your perspective. Alan Kay is alleged to have said
that a change of perspective is worth 80 IQ points...)
In this example, the top rule I'm using is:
ixml: s, rule++RS, s.
Where s is optional whitespace. And the rest of the grammar is a
reasonably close facsimile of the actual grammar; any minor exceptions
shouldn't matter for what follows.
The input is:
doc = "a", "b".
Including a newline at the end, that's 16 distinct Unicode characters
presented as input.
Here is the last few lines of completed traces of the parse: (numbers
after @ are the position after parsing that item. One-past-the-end, a la
C++ iterators)
430) 0:15👉 rule=( ---f-option78@0, name@3, s@4, -'='@5, s@6, -alts@14,
-'.'@15 • )
433) 15:15👉 --f-option72=( • )
438) 15:16👉 whitespace=( -'
'@16 • )
439) 15:15👉 --f-star71=( ---f-option72@15 • )
443) 16:16👉 --f-option77=( • )
441) 0:15👉 --f-plus-sep70=( rule@15, ---f-star71@15 • )
446) 16:16👉 --f-star76=( ---f-option77@16 • )
451) 15:15👉 --f-option74=( • )
448) 15:16👉 --f-plus75=( whitespace@16, ---f-star76@16 • )
453) 15:15👉 --f-star73=( ---f-option74@15 • )
454) 15:16👉 RS=( ---f-plus75@16 • )
455) 15:15👉 s=( ---f-star73@15 • )
459) 16:16👉 --f-option78=( • )
457) 0:15👉 ixml=( s@0, ---f-plus-sep70@15, s@15 • )
From the bottom up, the final trace 457) looks like the parse is in
good shape, I think. From character positions 0:15 we have a complete
match on the top ixml rule (which aligns with the the 'rule' match at
430), also at character positions 0:15). But to call it a success, the
code that processes this trace is looking for a complete 0:16 match on
the root rule 'ixml'.
There _is_ a 'whitespace' match 438) on a newline spanning 15:16, but
since the ixml rule ends with optional whitespace, the rule gets marked
as complete as seen here. Downstream code then errors out, since not all
of the input was matched by the root rule.
And 454) is interesting. There's still a leftover task on 'ixml' trying
to see if it can keep going.
The solution is at the tip of my cortex, but I'm just not seeing it.
Thoughts?
j
Received on Sunday, 18 September 2022 03:57:05 UTC