From: Rudolf Sykora <rudolf.sykora@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: [9fans] bison problem, not plan9 related
Date: Wed, 21 Oct 2009 19:52:41 +0200 [thread overview]
Message-ID: <a560a5d00910211052q2995c2afoae585c94f555947b@mail.gmail.com> (raw)
Hello,
sorry for an off-topic thing. But I guess somebody here could help me...
I have a problem with bison grammer
Having
%token ATOM
%left '+'
%left REP
and a grammar:
block: ATOM
| REP block
| block '+' block
;
is ok. Having another grammer:
block: ATOM
| REP block
| block block %prec '+'
;
has 2 shift/reduce conflicts, similar to
state 7
5 block: REP block .
6 | block . block
ATOM shift, and go to state 3
ATOM [reduce using rule 5 (block)]
$default reduce using rule 5 (block)
block go to state 9
or
state 9
6 block: block . block
6 | block block .
ATOM shift, and go to state 3
REP shift, and go to state 4
ATOM [reduce using rule 6 (block)]
$default reduce using rule 6 (block)
block go to state 9
What I want is to have a parser that can read e.g. (the spaces are
left out by lex, they are not in what bison sees; I only write them
here for better readability)
12 Au 13 Cu 2 Ag
the former grammer (REP is for repetition) is able to read
12 Au + 13 Cu + 2 Ag
but I don't like those pluses, which are redundant.
Also important: I have those 'block' non-terminals there, since I want
to add another rule
block: '[' block ']'
so that I can use brackets and can parse things like
12 [ 2 Cu 3 Co]
Could anyone explain to me what goes wrong?
I can't figure it out...
Thanks a lot
Ruda
PS.: the grammer is actually identical to a grammer that can evaluate
expressions with +, *, and brackets, with usual operator precedence.
next reply other threads:[~2009-10-21 17:52 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-21 17:52 Rudolf Sykora [this message]
2009-10-21 18:03 ` Rudolf Sykora
2009-10-21 18:46 ` Skip Tavakkolian
2009-10-21 19:44 ` Rudolf Sykora
2009-10-21 18:47 ` Russ Cox
2009-10-21 19:41 ` Rudolf Sykora
2009-10-21 19:48 ` Rudolf Sykora
2009-10-21 20:21 ` Russ Cox
2009-10-21 20:28 ` Rudolf Sykora
2009-10-21 20:03 ` Bakul Shah
2009-10-21 20:18 ` Rudolf Sykora
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