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Re: Different conflicts between byacc and bison

From: Domingo Alvarez Duarte
Subject: Re: Different conflicts between byacc and bison
Date: Thu, 4 Nov 2021 09:57:15 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0

Also tested with the latest byacc from https://invisible-island.net/byacc/:


./yacc -V
./yacc - 2.0 20210808

byacc-20210808/yacc gram.y
byacc-20210808/yacc: 21 shift/reduce conflicts, 3 reduce/reduce conflicts.


On 3/11/21 19:27, Domingo Alvarez Duarte wrote:
Hello !

I'm trying to build the CFRONT parser with bison instead of byacc and I've got bison to accept the grammar https://github.com/mingodad/cfront-3/blob/master/src/gram.y but the generated parser by bison has a small difference in the conflicts found in the grammar (see bellow) and also by comparison I tested the last C++ grammar from GCC 3.3.6 https://github.com/gcc-mirror/gcc/blob/releases/gcc-3.3.6/gcc/cp/parse.y and there byacc and bison seem to agree on the conflicts.

I tested with two bison versions and both give the same results but the generated parser do not pass the tests.

I'm pointing this here because it seems to be a good example of a corner case maybe not noticed so far.

bison (GNU Bison) 3.0.4
bison (GNU Bison) 3.8.2

byacc - 1.9 20140715


cfront-3/src$ bison -y gram.y
gram.y: warning: 20 shift/reduce conflicts [-Wconflicts-sr]
gram.y: warning: 4 reduce/reduce conflicts [-Wconflicts-rr]

cfront-3/srv$ byacc gram.y
byacc: 21 shift/reduce conflicts, 3 reduce/reduce conflicts.



gcc-3.3.6/gcc/cp$ bison -y parse.y
parse.y: warning: 33 shift/reduce conflicts [-Wconflicts-sr]
parse.y: warning: 58 reduce/reduce conflicts [-Wconflicts-rr]

gcc-3.3.6/gcc/cp$ byacc parse.y
byacc: 33 shift/reduce conflicts, 58 reduce/reduce conflicts.


Cheers !

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