Re: Change to shift instead of reduce

[Adam Smalin]

Could you give me a better example? I tried the below and neither helped. I
got the error

Ambiguity detected.
Option 1,
  mainLoop -> <Rule 5, tokens 1 .. 8>
    mainLoop -> <Rule 5, tokens 1 .. 7>
      mainLoop -> <Rule 5, tokens 1 .. 6>
        mainLoop <tokens 1 .. 4>
        mainElement -> <Rule 6, tokens 5 .. 6>
          '$' <tokens 5 .. 5>
          VarName <tokens 6 .. 6>
      mainElement -> <Rule 7, tokens 7 .. 7>
        mainElement2 -> <Rule 9, tokens 7 .. 7>
          Token -> <Rule 10, tokens 7 .. 7>
            '.' <tokens 7 .. 7>
    mainElement -> <Rule 7, tokens 8 .. 8>
      mainElement2 -> <Rule 8, tokens 8 .. 8>
        VAR <tokens 8 .. 8>

Option 2,
  mainLoop -> <Rule 5, tokens 1 .. 8>
    mainLoop <tokens 1 .. 4>
    mainElement -> <Rule 6, tokens 5 .. 8>
      '$' <tokens 5 .. 5>
      VarName -> <Rule 12, tokens 6 .. 8>
        VarName <tokens 6 .. 6>
        '.' <tokens 7 .. 7>
        VAR <tokens 8 .. 8>

>From both. Input is $a.b $a.b

%%
program: mEOS main
main: | mainLoop mEOS
mainLoop:
      mainElement            %dprec 5
    | mainLoop mainElement    %dprec 4
mainElement:
      %nonassoc '$' VarName    %dprec 6    { printf("varname\n"); }
    | mainElement2  %dprec 1
mainElement2:
      VAR             %dprec 3    { printf("var\n"); }
    | Token         %dprec 2    { printf("token\n"); }

Token: '.'            %dprec 1
VarName: VAR         %dprec 7
    | VarName  '.' VAR %dprec 8

EOS:   '\n' | ';'
mEOS:       | mEOS EOS

------

%right '$' '.'
%%
program: mEOS main
main: | mainLoop mEOS
mainLoop:
      mainElement            %prec 5
    | mainLoop mainElement    %prec 4
mainElement:
      '$' VarName    %dprec 6    { printf("varname\n"); }
    | mainElement2  %dprec 1
mainElement2:
      VAR             %dprec 3    { printf("var\n"); }
    | Token         %dprec 2    { printf("token\n"); }

Token: '.'            %dprec 1
VarName: VAR         %dprec 7
    | VarName  '.' VAR %dprec 8




On Mon, Jun 3, 2013 at 3:09 AM, Akim Demaille <address@hidden> wrote:

>
> Le 1 juin 2013 à 20:49, Adam Smalin <address@hidden> a écrit :
>
> > I have another thread but here is a simple version of my problem
> >
> > My text input is
> > a.b c.d
> > What I would like is
> > varname varname
> > My grammar is
> > %glr-parser
> > //...
> > mainLoop:
> >      mainElement            %dprec 5
> >    | mainLoop mainElement    %dprec 4
> > mainElement:
> >      '$' VarName    %dprec 6    { printf("varname\n"); }
> >    | VAR             %dprec 3    { printf("var\n"); }
> >    | Token         %dprec 2    { printf("token\n"); }
> >
> > Token: '.'            %dprec 1
> > VarName: VAR         %dprec 7
> >    | VarName '.' VAR %dprec 8
> >
> > The conflict file shows
> >    6 mainElement: '$' VarName .  [$end, VAR, '.', '$', '\n', ';']
> >   11 VarName: VarName . '.' VAR
> >
> >    '.'  shift, and go to state 18
> >
> >    '.'       [reduce using rule 6 (mainElement)]
> >    $default  reduce using rule 6 (mainElement)
> >
> > Now I see $default  reduce. I'd like it to shift. I threw in a bunch of
> > precedence hoping something would trigger a shift instead of a reduce but
> > no. What can I do?
>
> You have a competition between r6, which wants to be reduced,
> and token '.', which wants to be shifted.  r6 is "tagged" by
> '$', its rightmost token (use %prec to use another associativity
> / precedence carrier).  So you have a competition between "$" and ".".
> To make the latter win, several choices:
>
> - use precedence (e.g., %nonassoc '$' %nonassoc '.')
>
> - use associativity (to promote shift, make it right
>   associative: %right '$' '.').
>
> HTH.