lpeg.B(-n) patch for uncondtional backtrack
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: lpeg.B(-n) patch for uncondtional backtrack
- From: albertmcchan <albertmcchan@...>
- Date: 2018年1月27日 18:21:59 -0500
Finally bypassed the infinite recursion lpeg error checking.
(i treated %b as normal character, so be careful of infinite loops)
Now I can do this:
pat = re.compile "{ .* (g <- &'and' / %b g)} .^3 {.*}"
= pat:match "this and that and whatever"
this and that
whatever
---- Follwing is the patch if anyone interested (4 files) ----
>diff lpeg\re.lua lpeg-1.0.1\re.lua
27c27
< local Predef = { nl = m.P"\n", b = m.B(-1) }
---
> local Predef = { nl = m.P"\n" }
>diff lpeg\lptree.c lpeg-1.0.1\lptree.c
430d429
< tree->u.n = n; // possibly lpeg.B(-n)
689,690c688
< // lpeg.B(-n) = behind n
< tree->u.n = (sib1(tree)->tag == TNot) ? sib1(tree)->u.n : n;
---
> tree->u.n = n;
1008,1009d1005
< case TBehind: /* look-ahead cannot have calls */
< if (sib1(tree)->tag != TNot) return 1;
1013a1010
> case TBehind: /* look-ahead cannot have calls */
>diff lpeg\lpcode.c lpeg-1.0.1\lpcode.c
204,206c204
< case TBehind: // lpeg.B(-n) not nullable
< if (sib1(tree)->tag == TNot) return 0;
< case TNot: // fall thru for lpeg.B(n)
---
> case TNot: case TBehind: /* can match empty, but can fail */
664d661
< if (sib1(tree)->tag != TNot) // lpeg.B(-n) = behind n
>diff lpeg\lpprint.c lpeg-1.0.1\lpprint.c
185d184
< if (sib1(tree)->tag != TNot) // lpeg.B(-n) = behind n