Re: Lpeg error handling
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- Subject: Re: Lpeg error handling
- From: Miles Bader <miles@...>
- Date: 2009年4月22日 15:58:07 +0900
Ico <lua@zevv.nl> writes:
> My problem is that I'm not sure how to handle parsing errors gracefully.
> If there's a single syntax error somewhere in the file, the Lpeg pattern
> does not match at all, so the application is only able to inform the
> user that "there is a syntax error somewehere", but no details about the
> exact location. Instead I'd like my app to be able to at least report
> the line number to the user when the parser finds an error.
[The following is a repeat of an old reply I gave to a similar query.]
I use a function matcher that records the current position, e.g.:
local function update_err_pos (text, pos)
parse_state.err_pos = pos
return pos
end
-- This special lpeg pattern updates the current error position
--
ERR_POS = P(update_err_pos)
[where "parse_state" is some global; probably better ways to do that
now, e.g., the special capture you can use to access the Nth arg of the
lpeg match call]
Then I stick ERR_POS in various places, for instance, after the
end-of-line pattern... e.g.:
-- this matches a newline, and also updates the error location
local WS_NL_SYNC = WS_NL * lu.ERR_POS
The error reporting routines then use the error position to find the
last line that was ever matched, and include that information along with
the error message.
-Miles
--
80% of success is just showing up. --Woody Allen