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GLR: ambiguity reports are wrong
From: |
Akim Demaille |
Subject: |
GLR: ambiguity reports are wrong |
Date: |
Tue, 21 Feb 2012 12:20:46 +0100 |
On this grammar:
> %%
> start:
> 'a' b 'c' d
> | 'a' b 'c' d
> ;
> b: 'b';
> d: /* nada. */;
> %%
with input a b c d, the current code reports:
> Option 1,
> start -> <Rule 1, tokens 1 .. 3>
> $end <tokens 1 .. 1>
> 'a' <tokens 2 .. 2>
> b <tokens 3 .. 3>
> 'c' <empty>
>
> Option 2,
> start -> <Rule 2, tokens 1 .. 3>
> $end <tokens 1 .. 1>
> 'a' <tokens 2 .. 2>
> b <tokens 3 .. 3>
> 'c' <empty>
instead of:
> Option 1,
> start -> <Rule 1, tokens 1 .. 3>
> 'a' <tokens 1 .. 1>
> b <tokens 2 .. 2>
> 'c' <tokens 3 .. 3>
> d <empty>
>
> Option 2,
> start -> <Rule 2, tokens 1 .. 3>
> 'a' <tokens 1 .. 1>
> b <tokens 2 .. 2>
> 'c' <tokens 3 .. 3>
> d <empty>
This is a regression I introduced in master only with
commit 783aa653f4ca70a75919c8516b950494c612cbfe.
http://lists.gnu.org/archive/html/bison-patches/2008-11/msg00291.html
0001-glr-fix-ambiguity-reports.patch
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