Re: How to read an understand the bison report file ?

[Akim Demaille]

Le 27 juin 2012 à 08:00, Akim Demaille a écrit :

> For instance, you have:
> 
> state 88
> 
>    1 t_comment_or_whitespace: . T_WHITESPACE
>    2                        | . T_COMMENT
>    3 plain_comment_or_whitespace: . t_comment_or_whitespace
>    4                            | . plain_comment_or_whitespace 
> t_comment_or_whitespace
>    5 t_comment_or_whitespaces: .  [T_BOOLEAN_OR]
>    6                         | . plain_comment_or_whitespace
>   90 boolean_or_expr: boolean_or_expr . t_comment_or_whitespaces T_BOOLEAN_OR 
> t_comment_or_whitespaces boolean_and_expr
>   91 conditional_expression: boolean_or_expr .  [T_CLOSE_TAG, T_AS, 
> T_WHITESPACE, T_COMMENT, T_LOGICAL_AND, T_LOGICAL_OR, T_LOGICAL_XOR, 
> T_DOUBLE_ARROW, "+= (T_PLUS_EQUAL)", "-= (T_MINUS_EQUAL)", "*= 
> (T_MUL_EQUAL)", "/= (T_DIV_EQUAL)", ".= (T_CONCAT_EQUAL)", "%= 
> (T_MOD_EQUAL)", "&= (T_AND_EQUAL)", "|= (T_OR_EQUAL)", "^= (T_XOR_EQUAL)", 
> "<<= (T_SL_EQUAL)", ">>= (T_SR_EQUAL)", '}', ':', ',', ')', ']', '?', '=', 
> ';']
> 
>    T_WHITESPACE  shift, and go to state 1
>    T_COMMENT     shift, and go to state 2
> 
>    T_WHITESPACE  [reduce using rule 91 (conditional_expression)]
>    T_COMMENT     [reduce using rule 91 (conditional_expression)]
>    T_BOOLEAN_OR  reduce using rule 5 (t_comment_or_whitespaces)
>    $default      reduce using rule 91 (conditional_expression)
> 
>    t_comment_or_whitespace      go to state 3
>    plain_comment_or_whitespace  go to state 4
>    t_comment_or_whitespaces     go to state 169
> 
> which means that Bison does not know whether to reduce or to shift
> when a whitespace or a comment arrives after a boolean_or_expr.

Actually I realize that I answered without paying too much
attention to your grammar, and in the present case, always
shifting is not the right answer, nor is always-reducing:

>   90 boolean_or_expr: boolean_or_expr . t_comment_or_whitespaces T_BOOLEAN_OR 
> t_comment_or_whitespaces boolean_and_expr
>   91 conditional_expression: boolean_or_expr .  [T_WHITESPACE, T_COMMENT, …]

There is no way to know whether _after_ the whitespace/comment
there is a T_BOOLEAN_OR.  Your grammar is not LR(1), not even
LR(k) as there can be as many whitespace/comment as you
want after boolean_or_expr, and before the token that will
help deciding whether to chose rule 90 (T_BOOLEAN_OR) or rule 91
(otherwise).

Either you need to completely change the way you handle the
spaces/comments, or you have to use GLR, as Hans suggested.