Problem with precedence and symbolic tokens

I am trying to use precedences in Bison. After several
trials, a
simplified version of the relevant part of my input file is
(it is
supposed to produce reversed Polish notation):

------------------------------------------------------------
------------------------
%{ ... %}

%left ADD
%left MULT
%right EXP
%left UNARY

%%
...
Expr
        : Expr AddOp  Expr   %prec ADD    {
printf("+"); }
        | Expr MultOp Expr   %prec MULT   {
printf("*"); }
        | Expr ExpOp  Expr   %prec EXP     {
printf("^"); }
        | 'a'                                              
{ printf("a"); }
        | '(' Expr ')'
        | '-' Expr                  %prec UNARY  {
printf("~"); }
        ;
AddOp
        :  '+'
        |  '-'
        ;
MultOp
        :  '*'
        |  '/'
ExpOp
        :  '^'
        ;
%%
...
------------------------------------------------------------
------------------

Unfortunately precedences do not seem to work. On the other
hand, if I
replace operator nonterminals by (like Addop) their symbols
('+') and
put specs like %left '+', it works (without any %prec).

Any hints?

-- tsf


_______________________________________________
help-bisongnu.org http
://lists.gnu.org/mailman/listinfo/help-bison

It just looks at the tokens in the rules, so you can't throw
in extra  
rules like you have done below. That is, AddOp must be
expanded into  
two rules "Expr: ...".

Look in the .outout file for the S/R conflicts, and the
tokens  
immediately before and after the parsing position dot
".".

   Hans Aberg


On 17 Mar 2008, at 19:30, T. S. Ferreira wrote:

> I am trying to use precedences in Bison. After several
trials, a
> simplified version of the relevant part of my input
file is (it is
> supposed to produce reversed Polish notation):
>
>
------------------------------------------------------------
---------- 
> --------------
> %{ ... %}
>
> %left ADD
> %left MULT
> %right EXP
> %left UNARY
>
> %%
> ...
> Expr
>         : Expr AddOp  Expr   %prec ADD    {
printf("+"); }
>         | Expr MultOp Expr   %prec MULT   {
printf("*"); }
>         | Expr ExpOp  Expr   %prec EXP     {
printf("^"); }
>         | 'a'                                          
    { printf 
> ("a"); }
>         | '(' Expr ')'
>         | '-' Expr                  %prec UNARY  {
printf("~"); }
>         ;
> AddOp
>         :  '+'
>         |  '-'
>         ;
> MultOp
>         :  '*'
>         |  '/'
> ExpOp
>         :  '^'
>         ;
> %%
> ...
>
------------------------------------------------------------
---------- 
> --------
>
> Unfortunately precedences do not seem to work. On the
other hand, if I
> replace operator nonterminals by (like Addop) their
symbols ('+') and
> put specs like %left '+', it works (without any
%prec).
>
> Any hints?
>
> -- tsf
>
>
> _______________________________________________
> help-bisongnu.org http
://lists.gnu.org/mailman/listinfo/help-bison



_______________________________________________
help-bisongnu.org http
://lists.gnu.org/mailman/listinfo/help-bison

I got it. My application has lots of operators and I was
looking for
some way of simplifying my grammar but there seems to be no
other way.

Thanks a lot.

-- tsf


On Mon, Mar 17, 2008 at 3:51 PM, Hans Aberg <habergmath.su.se> wrote:
> It just looks at the tokens in the rules, so you can't
throw in extra
>  rules like you have done below. That is, AddOp must be
expanded into
>  two rules "Expr: ...".
>
>  Look in the .outout file for the S/R conflicts, and
the tokens
>  immediately before and after the parsing position dot
".".
>
>    Hans Aberg
>
>
>
>
>  On 17 Mar 2008, at 19:30, T. S. Ferreira wrote:
>
>  > I am trying to use precedences in Bison. After
several trials, a
>  > simplified version of the relevant part of my
input file is (it is
>  > supposed to produce reversed Polish notation):
>  >
>  >
------------------------------------------------------------
----------
>  > --------------
>  > %{ ... %}
>  >
>  > %left ADD
>  > %left MULT
>  > %right EXP
>  > %left UNARY
>  >
>  > %%
>  > ...
>  > Expr
>  >         : Expr AddOp  Expr   %prec ADD    {
printf("+"); }
>  >         | Expr MultOp Expr   %prec MULT   {
printf("*"); }
>  >         | Expr ExpOp  Expr   %prec EXP     {
printf("^"); }
>  >         | 'a'                                    
          { printf
>  > ("a"); }
>  >         | '(' Expr ')'
>  >         | '-' Expr                  %prec UNARY 
{ printf("~"); }
>  >         ;
>  > AddOp
>  >         :  '+'
>  >         |  '-'
>  >         ;
>  > MultOp
>  >         :  '*'
>  >         |  '/'
>  > ExpOp
>  >         :  '^'
>  >         ;
>  > %%
>  > ...
>  >
------------------------------------------------------------
----------
>  > --------
>  >
>  > Unfortunately precedences do not seem to work. On
the other hand, if I
>  > replace operator nonterminals by (like Addop)
their symbols ('+') and
>  > put specs like %left '+', it works (without any
%prec).
>  >
>  > Any hints?
>  >
>  > -- tsf
>  >
>  >
>  > _______________________________________________
>  > help-bisongnu.org http
://lists.gnu.org/mailman/listinfo/help-bison
>
>



-- 
T. S. Ferreira


_______________________________________________
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