c - 为什么我在这个 bison 语法中收到这么多 'useless rule/token' 警告？

Question

我正在为 C 编写一个简单的 bison 语法，到目前为止有以下规则:

program                 : declaration_list
                        ;

declaration_list        : declaration_list declaration
                        | declaration
                        ;

declaration             : var_declaration
                        | fun_declaration
                        ;

var_declaration         : type_specifier var_decl_list EOL
                        ;

scoped_var_declaration  : scoped_type_specifier var_decl_list EOL
                        ;

var_decl_list           : var_decl_list COMMA var_decl_initialise
                        | var_decl_initialise
                        ;

var_decl_initialise     : var_decl_id
                        | var_decl_id COLON simple_expression
                        ;

var_decl_id             : ID
                        | ID LSQUARE INT_VAL RSQUARE
                        ;

scoped_type_specifier   : type_specifier
                        ;

type_specifier          : INT
                        | FLOAT
                        | DOUBLE
                        | CHAR
                        | BOOL
                        ;

fun_declaration         : type_specifier ID LPAREN params RPAREN 
                        | ID LPAREN params RPAREN statement
                        ;

params                  : /*Empty*/
                        | param_list
                        ;

param_list              : param_list EOL param_type_list
                        | param_type_list
                        ;

param_type_list         : type_specifier param_id_list
                        ;

param_id_list           : param_id_list COMMA param_id
                        | param_id
                        ;

param_id                : ID
                        | ID LSQUARE RSQUARE
                        ;

statement               : expression_stmt
                        | compound_stmt
                        | selection_stmt
                        | iteration_stmt
                        | return_stmt
                        | break_stmt
                        ;

compound_stmt           : LBRACE local_declarations statement_list RBRACE 
                        ;

local_declarations      : /*Empty*/
                        | local_declarations scoped_var_declaration
                        ;

statement_list          : /*Empty*/
                        | statement_list statement
                        ;

expression_stmt         : expression EOL
                        | EOL
                        ;

selection_stmt          : IF LPAREN simple_expression RPAREN statement
                        | IF LPAREN simple_expression RPAREN statement ELSE statement
                        ;

iteration_stmt          : WHILE LPAREN simple_expression RPAREN statement // TODO: for
                        ;

return_stmt             : RETURN EOL
                        | RETURN expression EOL
                        ;

break_stmt              : BREAK EOL
                        ;

expression              : mutable '=' expression
                        | mutable ADD_ASSIGN expression
                        | mutable SUB_ASSIGN expression
                        | mutable '*' expression
                        | mutable DIV_ASSIGN expression
                        | mutable BITWISE_AND_ASSIGN expression
                        | mutable BITWISE_OR_ASSIGN expression
                        | mutable INCREMENT
                        | mutable DECREMENT
                        | simple_expression
                        ;

simple_expression       : simple_expression LOGICAL_OR and_expression
                        | and_expression
                        ;

and_expression          : and_expression LOGICAL_AND unary_rel_expression
                        | and_expression
                        ;

unary_rel_expression    : '!' unary_rel_expression
                        | rel_expression
                        ;

rel_expression          : sum_expression relop sum_expression
                        | sum_expression
                        ;

relop                   : LT_EQUAL_TO
                        | '<'
                        | '>'
                        | GT_EQUAL_TO
                        | EQUAL_TO
                        | NOT_EQUAL_TO
                        ;

sum_expression          : sum_expression sumop term
                        | term
                        ;

sumop                   : '+' 
                        | '-'
                        ;

term                    : term mulop unary_expression
                        | unary_expression
                        ;

mulop                   : '*'
                        | '/'
                        | '%'
                        ;

unary_expression        : unaryop unary_expression
                        | factor
                        ;

unaryop                 : '-' 
                        | '*'
                        ;

factor                  : immutable
                        | mutable
                        ;

mutable                 : ID 
                        | ID LSQUARE expression RSQUARE
                        ;

immutable               : LPAREN expression RPAREN 
                        | call 
                        | constant
                        ;

call                    : ID LPAREN args RPAREN
                        ;

args                    : /*Empty*/
                        | arg_list
                        ;

arg_list                : arg_list COMMA expression
                        | expression
                        ;

constant                : number
                        | boolean
                        | CHAR_VAL
                        | STRING_VAL
                        ;

number                  : INT_VAL
                        | DOUBLE_VAL
                        ;

boolean                 : TRUE
                        | FALSE
                        ;

但是当我尝试用 bison 编译时，我收到一大堆警告，说几乎所有的规则和标记都是无用的:

parser.y: warning: 21 nonterminals useless in grammar
parser.y: warning: 52 rules useless in grammar
parser.y:127.27-40: warning: nonterminal useless in grammar: selection_stmt
parser.y:128.27-40: warning: nonterminal useless in grammar: iteration_stmt
parser.y:85.45-61: warning: nonterminal useless in grammar: simple_expression
parser.y:174.56-69: warning: nonterminal useless in grammar: and_expression
parser.y:178.54-73: warning: nonterminal useless in grammar: unary_rel_expression
parser.y:183.27-40: warning: nonterminal useless in grammar: rel_expression
parser.y:186.42-46: warning: nonterminal useless in grammar: relop
parser.y:186.27-40: warning: nonterminal useless in grammar: sum_expression
parser.y:198.42-46: warning: nonterminal useless in grammar: sumop
parser.y:198.48-51: warning: nonterminal useless in grammar: term
parser.y:206.32-36: warning: nonterminal useless in grammar: mulop
parser.y:206.38-53: warning: nonterminal useless in grammar: unary_expression
parser.y:215.27-33: warning: nonterminal useless in grammar: unaryop
parser.y:216.27-32: warning: nonterminal useless in grammar: factor
parser.y:223.27-35: warning: nonterminal useless in grammar: immutable
parser.y:232.27-30: warning: nonterminal useless in grammar: call
parser.y:236.37-40: warning: nonterminal useless in grammar: args
parser.y:240.27-34: warning: nonterminal useless in grammar: arg_list
parser.y:233.27-34: warning: nonterminal useless in grammar: constant
parser.y:247.27-32: warning: nonterminal useless in grammar: number
parser.y:248.27-33: warning: nonterminal useless in grammar: boolean
parser.y:85.27-61: warning: rule useless in grammar: var_decl_initialise: var_decl_id COLON simple_expression
parser.y:127.27-40: warning: rule useless in grammar: statement: selection_stmt
parser.y:128.27-40: warning: rule useless in grammar: statement: iteration_stmt
parser.y:148.27-70: warning: rule useless in grammar: selection_stmt: IF LPAREN simple_expression RPAREN statement
parser.y:149.27-85: warning: rule useless in grammar: selection_stmt: IF LPAREN simple_expression RPAREN statement ELSE statement
parser.y:152.27-73: warning: rule useless in grammar: iteration_stmt: WHILE LPAREN simple_expression RPAREN statement
parser.y:171.27-43: warning: rule useless in grammar: expression: simple_expression
parser.y:174.27-69: warning: rule useless in grammar: simple_expression: simple_expression LOGICAL_OR and_expression
parser.y:175.27-40: warning: rule useless in grammar: simple_expression: and_expression
parser.y:178.27-73: warning: rule useless in grammar: and_expression: and_expression LOGICAL_AND unary_rel_expression
parser.y:179.27-40: warning: rule useless in grammar: and_expression: and_expression
parser.y:182.27-50: warning: rule useless in grammar: unary_rel_expression: '!' unary_rel_expression
parser.y:183.27-40: warning: rule useless in grammar: unary_rel_expression: rel_expression
parser.y:186.27-61: warning: rule useless in grammar: rel_expression: sum_expression relop sum_expression
parser.y:187.27-40: warning: rule useless in grammar: rel_expression: sum_expression
parser.y:190.27-37: warning: rule useless in grammar: relop: LT_EQUAL_TO
parser.y:191.27-29: warning: rule useless in grammar: relop: '<'
parser.y:192.27-29: warning: rule useless in grammar: relop: '>'
parser.y:193.27-37: warning: rule useless in grammar: relop: GT_EQUAL_TO
parser.y:194.27-34: warning: rule useless in grammar: relop: EQUAL_TO
parser.y:195.27-38: warning: rule useless in grammar: relop: NOT_EQUAL_TO
parser.y:198.27-51: warning: rule useless in grammar: sum_expression: sum_expression sumop term
parser.y:199.27-30: warning: rule useless in grammar: sum_expression: term
parser.y:202.27-29: warning: rule useless in grammar: sumop: '+'
parser.y:203.27-29: warning: rule useless in grammar: sumop: '-'
parser.y:206.27-53: warning: rule useless in grammar: term: term mulop unary_expression
parser.y:207.27-42: warning: rule useless in grammar: term: unary_expression
parser.y:210.27-29: warning: rule useless in grammar: mulop: '*'
parser.y:211.27-29: warning: rule useless in grammar: mulop: '/'
parser.y:212.27-29: warning: rule useless in grammar: mulop: '%'
parser.y:215.27-50: warning: rule useless in grammar: unary_expression: unaryop unary_expression
parser.y:216.27-32: warning: rule useless in grammar: unary_expression: factor
parser.y:219.27-29: warning: rule useless in grammar: unaryop: '-'
parser.y:220.27-29: warning: rule useless in grammar: unaryop: '*'
parser.y:223.27-35: warning: rule useless in grammar: factor: immutable
parser.y:224.27-33: warning: rule useless in grammar: factor: mutable
parser.y:231.27-50: warning: rule useless in grammar: immutable: LPAREN expression RPAREN
parser.y:232.27-30: warning: rule useless in grammar: immutable: call
parser.y:233.27-34: warning: rule useless in grammar: immutable: constant
parser.y:236.27-47: warning: rule useless in grammar: call: ID LPAREN args RPAREN
parser.y:239.5: warning: rule useless in grammar: args: /* empty */
parser.y:240.27-34: warning: rule useless in grammar: args: arg_list
parser.y:243.27-51: warning: rule useless in grammar: arg_list: arg_list COMMA expression
parser.y:244.27-36: warning: rule useless in grammar: arg_list: expression
parser.y:247.27-32: warning: rule useless in grammar: constant: number
parser.y:248.27-33: warning: rule useless in grammar: constant: boolean
parser.y:249.27-34: warning: rule useless in grammar: constant: CHAR_VAL
parser.y:250.27-36: warning: rule useless in grammar: constant: STRING_VAL
parser.y:253.27-33: warning: rule useless in grammar: number: INT_VAL
parser.y:254.27-36: warning: rule useless in grammar: number: DOUBLE_VAL
parser.y:257.27-30: warning: rule useless in grammar: boolean: TRUE
parser.y:258.27-31: warning: rule useless in grammar: boolean: FALSE

我花了好几个小时查看它，并尝试检查使用选项 -r all 运行 bison 时获得的 .output 文件，但我无法弄清楚我的错误在哪里马德群岛我知道“无用”意味着永远不会达到规则，但我看不到断开连接的位置。

Answer 1

第175行有错字，我想应该是这样的:

and_expression          : and_expression LOGICAL_AND unary_rel_expression
                        | unary_rel_expression
                        ;

...警告将消失。