bison - 野牛难悬垂的其他去除

Question

我正试图摆脱我语法中的其他悬而未决的东西。终端是大写字母。我有：

statement:
    expression_statement (not important now )
    | compound_statement (not important now )
    | selection_statement
    | iteration_statement (not important now but maybe yes ? it contains statement non-terminal )
    | jump_statement (not important now )
    ;

selection_statement:
    IF LPAR expression RPAR statement
    | IF LPAR expression RPAR statement ELSE statement
    ;

iteration_statement:
    WHILE LPAR expression RPAR statement
    | DO statement WHILE LPAR expression RPAR SEMIC
    | FOR LPAR expression_opt SEMIC expression_opt SEMIC expression_opt RPAR statement
    ;

我试过这种方法

statement:
    expression_statement
    | compound_statement
    | selection_statement_o
    | selection_statement_c
    | iteration_statement
    | jump_statement
    ;

selection_statement_o:
    IF LPAR expression RPAR statement
    | IF LPAR expression RPAR selection_statement_c ELSE selection_statement_o
    ;

selection_statement_c:
    IF LPAR expression RPAR selection_statement_c ELSE selection_statement_c
    ;

我现在被卡住了，不知道该怎么办。我应该如何在这里正确地移除悬空的 else ？谢谢你的帮助。

编辑1：我尝试了这种方法，我得到了更少的移位/减少冲突和更多的减少/减少冲突我想这是不对的：D但它是

statement:
    matched
    | unmatched
    | other
    ;

other:
    expression_statement
    | compound_statement
    | jump_statement
    ;

matched:
    selection_statement_c
    | iteration_statement_c
    ;

unmatched:
    selection_statement_o
    | iteration_statement_o
    ;

selection_statement_o:
    IF LPAR expression RPAR statement
    | IF LPAR expression RPAR matched ELSE unmatched
    ;

selection_statement_c:
    IF LPAR expression RPAR matched ELSE matched
    ;

iteration_statement_o:
    WHILE LPAR expression RPAR unmatched
    | DO statement WHILE LPAR expression RPAR SEMIC
    | FOR LPAR expression_opt SEMIC expression_opt SEMIC expression_opt RPAR unmatched
    ;

iteration_statement_c:
    WHILE LPAR expression RPAR matched
    | DO statement WHILE LPAR expression RPAR SEMIC
    | FOR LPAR expression_opt SEMIC expression_opt SEMIC expression_opt RPAR matched
    ;

标签： bisonambiguous-grammardangling-else