Re: lpeg.U ?
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- Subject: Re: lpeg.U ?
- From: Sean Conner <sean@...>
- Date: 2018年1月25日 22:52:28 -0500
It was thus said that the Great albertmcchan once stated:
> i am using lpeg 1.0.1, and it has lpeg.code, which call lp_printcode in lptree.c
Ah, I did not see it when I scanned the source code.
> the code is just an example of the usefulness of undo
I still think you approaching LPeg as a replacement for patterns instead
of a tool for semantically parsing text.
> FYI, the last 'and' may not be anchored in end-of-string.
> If you remove the anchor, you got the first 'and', not the last
>
> i was just curious if undo is possible ...
"Undo" what? If you have an expression:
A * ( B + C )
A is matched. Then B is tried. If that fails, LPeg will "undo" B and try
C. That's an "undo". You also have look-ahead with the '#' operator (and
to some degree with the '-' operator).
I know, you are trying to do:
(.*)and(.*)
and have it replicate a Lua pattern. Yes, you can do that. There have been
several versions doing so. But (and this is something I can't repeat
enough) you need to think differently with LPeg---think "structure" and not
just "pattern". Compare this:
https://github.com/spc476/LPeg-talk/blob/master/email-addr.lua
with this:
http://www.ex-parrot.com/~pdw/Mail-RFC822-Address.html
to parse email addresses as defined in RFC-822 (the LPeg one can handle
comments; the regex one can't).
-spc (So I ask again, what exactly are you trying to do?)