Help Resolving Shift Reduce Conflicts In Bison Grammar

"Fraser Orr" <ifo@xnet.com>
29 May 2001 23:57:21 -0400

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Help Resolving Shift Reduce Conflicts In Bison Grammar ifo@xnet.com (Fraser Orr) (2001-05-29)
Re: Help Resolving Shift Reduce Conflicts In Bison Grammar chrisd@reservoir.com (2001-05-31)
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From: "Fraser Orr" <ifo@xnet.com>
Newsgroups: comp.compilers
Date: 29 May 2001 23:57:21 -0400
Organization: XNet Information Systems (Winstar)
Keywords: parse, question
Posted-Date: 29 May 2001 23:57:21 EDT

I have a simple grammar that parses a small language similar
to HTML. A fragment looks something like this:


%token PARA PARA_END BOLD BOLD_END TEXTBLOCK
%%
text : /* empty */
        | text textElement


textElement: inlineElement
                        | paragraph


inlineText : /* empty */
                        | inlineText inlineElement


inlineElement : TEXTBLOCK
                        | BOLD inlineText BOLD_END


paragraph: PARA inlineText optParaEnd


optParaEnd: /* empty */
                    | PARA_END


This produces two shift reduce conflicts. The problem
being that the grammar does not specify how to group a
sequence of inlineElement. For example:


<P> textblock1 textblock2


when parsed at text can either resolve to
              (PARA textblock1) textblock2
or
              (PARA textblock1 textblock2)


The latter is correct, that is the shift is correct behavior,
however, I would like to eliminate the shift reduce conflict
since this problem is spreading all over the grammar. Does
anyone have a suggestion?


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