建立野牛語法時，終端上顯示了太多無用的規則
[英]too many useless rules show up on terminal while building a bison grammar
問題描述
編碼：
%{
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include "gener.h"
#include "sym_tab.h"
#include "scope.h"
#include "defs.h"
extern char *yytext;
#define YYPRINT(file, type, value) yyprint (file, type, value)
%}
%union
{
char *name;
char idtype;
decl_list idlist;
/*decl_list is in gener.h,
you should #include "gener.h"
*/
}
%token PROGRAM
%token IDENTIFIER
%token DECIMAL_CONSTANT
%token DECLARE ENDDECLARE
%token AND CALL DEFAULT
%token FUNCTION PROCEDURE IN INOUT
%token IF ELSE DO WHILE FOR OR NOT SELECT
%token RETURN EXIT PRINT
%token EQ_LT EQ_GT NE EXACT
%left '+' '-'
%right '*' '/'
%start program
%%
program
: %empty
| PROGRAM IDENTIFIER block
;
block
: "{" declarations subprograms sequence "}"
;
declarations
: %empty
| DECLARE varlist ENDDECLARE
;
varlist
: %empty
| assignment_stat identifier2
;
identifier2 : ',' assignment_stat
| ',' assignment_stat
;
subprograms
: func
| subprograms ','
;
func
: PROCEDURE IDENTIFIER funcbody
| FUNCTION IDENTIFIER funcbody
;
funcbody
: formalpars block
;
formalpars
: '('')'
| '(' formalparlist ')'
;
formalparlist
: formalparitem
| formalparlist ','
;
formalparitem
: IN IDENTIFIER
| INOUT IDENTIFIER
;
sequence
: statement statement_sequence
;
statement_sequence
: ";"statement
| ';' statement statement_sequence
;
brackets_seq
: '{' sequence '}'
;
brack_or_stat
: brackets_seq
| statement
;
statement
: %empty
| assignment_stat
| if_stat
| do_while_stat
| while_stat
| select_stat
| exit_stat
| return_stat
| print_stat
| call_stat
;
assignment_stat
: IDENTIFIER EXACT IDENTIFIER
;
if_stat
: IF '(' condition')' brack_or_stat elsepart
;
elsepart
: %empty
| ELSE brack_or_stat
;
while_stat
: WHILE '(' condition')' brack_or_stat
;
select_stat
: SELECT'(' IDENTIFIER')'
dec
DEFAULT":" brack_or_stat
;
dec
: DECIMAL_CONSTANT ':' brack_or_stat
| dec ','
;
do_while_stat
: DO brack_or_stat WHILE '(' condition ')'
;
exit_stat
: EXIT
;
return_stat
: RETURN '(' expression ')'
;
print_stat
: PRINT '('expression ')'
;
call_stat
: CALL IDENTIFIER actualpars
;
actualpars
: '('')'
| '('actualparlist')'
;
actualparlist
: actualparitem
| actualparlist ','
;
actualparitem
: IN expression
| INOUT IDENTIFIER
;
condition
: boolterm or_boolterm
;
or_boolterm
: OR boolterm
| OR boolterm or_boolterm
;
boolterm
: boolfactor and_boolfactor
;
and_boolfactor
: AND boolfactor
| AND boolfactor and_boolfactor
;
boolfactor
: NOT '[' condition ']'
| '[' condition ']'
| expression relational_oper expression
;
expression
: optional_sign term add_oper_term
;
add_oper_term
: add_oper term
| add_oper term add_oper_term
;
term
: factor mul_oper_factor
;
mul_oper_factor
: mul_oper factor
| mul_oper factor mul_oper_factor
;
factor
: DECIMAL_CONSTANT
| expression
| IDENTIFIER idtail
;
idtail
: %empty
| actualpars
;
relational_oper
: '='
| '<'
| "<="
| "<>"
| ">="
| '>'
;
add_oper
: '+'
| '-'
;
mul_oper
: '*'
| '/'
;
optional_sign
: add_oper
| %empty
;
%%
這是我為野牛創建的語法，但是當我在終端上嘗試野牛gram.y時，會出現一堆警告。 試圖切換他們被寫的順序，但我仍然得到同樣的東西這里是終端輸出
gram.y: warning: 44 nonterminals useless in grammar [-Wother]
gram.y: warning: 86 rules useless in grammar [-Wother]
gram.y:43.38-42: warning: nonterminal useless in grammar: block [-Wother]
| PROGRAM IDENTIFIER block
^^^^^
gram.y:47.23-34: warning: nonterminal useless in grammar: declarations [-Wother]
: "{" declarations subprograms sequence "}"
^^^^^^^^^^^^
gram.y:51.27-33: warning: nonterminal useless in grammar: varlist [-Wother]
| DECLARE varlist ENDDECLARE
^^^^^^^
gram.y:55.35-45: warning: nonterminal useless in grammar: identifier2 [-Wother]
| assignment_stat identifier2
^^^^^^^^^^^
gram.y:47.36-46: warning: nonterminal useless in grammar: subprograms [-Wother]
: "{" declarations subprograms sequence "}"
^^^^^^^^^^^
gram.y:63.19-22: warning: nonterminal useless in grammar: func [-Wother]
: func
^^^^
gram.y:67.40-47: warning: nonterminal useless in grammar: funcbody [-Wother]
: PROCEDURE IDENTIFIER funcbody
^^^^^^^^
gram.y:71.19-28: warning: nonterminal useless in grammar: formalpars [-Wother]
: formalpars block
^^^^^^^^^^
gram.y:75.23-35: warning: nonterminal useless in grammar: formalparlist [-Wother]
| '(' formalparlist ')'
^^^^^^^^^^^^^
gram.y:79.19-31: warning: nonterminal useless in grammar: formalparitem [-Wother]
: formalparitem
^^^^^^^^^^^^^
gram.y:47.48-55: warning: nonterminal useless in grammar: sequence [-Wother]
: "{" declarations subprograms sequence "}"
^^^^^^^^
gram.y:88.29-46: warning: nonterminal useless in grammar: statement_sequence [-Wother]
: statement statement_sequence
^^^^^^^^^^^^^^^^^^
gram.y:94.1-12: warning: nonterminal useless in grammar: brackets_seq [-Wother]
brackets_seq
^^^^^^^^^^^^
gram.y:97.1-13: warning: nonterminal useless in grammar: brack_or_stat [-Wother]
brack_or_stat
^^^^^^^^^^^^^
gram.y:88.19-27: warning: nonterminal useless in grammar: statement [-Wother]
: statement statement_sequence
^^^^^^^^^
gram.y:55.19-33: warning: nonterminal useless in grammar: assignment_stat [-Wother]
| assignment_stat identifier2
^^^^^^^^^^^^^^^
gram.y:106.19-25: warning: nonterminal useless in grammar: if_stat [-Wother]
| if_stat
^^^^^^^
gram.y:120.53-60: warning: nonterminal useless in grammar: elsepart [-Wother]
: IF '(' condition')' brack_or_stat elsepart
^^^^^^^^
gram.y:108.19-28: warning: nonterminal useless in grammar: while_stat [-Wother]
| while_stat
^^^^^^^^^^
gram.y:109.19-29: warning: nonterminal useless in grammar: select_stat [-Wother]
| select_stat
^^^^^^^^^^^
gram.y:131.19-21: warning: nonterminal useless in grammar: dec [-Wother]
dec
^^^
gram.y:107.19-31: warning: nonterminal useless in grammar: do_while_stat [-Wother]
| do_while_stat
^^^^^^^^^^^^^
gram.y:110.19-27: warning: nonterminal useless in grammar: exit_stat [-Wother]
| exit_stat
^^^^^^^^^
gram.y:111.19-29: warning: nonterminal useless in grammar: return_stat [-Wother]
| return_stat
^^^^^^^^^^^
gram.y:112.19-28: warning: nonterminal useless in grammar: print_stat [-Wother]
| print_stat
^^^^^^^^^^
gram.y:113.19-27: warning: nonterminal useless in grammar: call_stat [-Wother]
| call_stat
^^^^^^^^^
gram.y:151.35-44: warning: nonterminal useless in grammar: actualpars [-Wother]
: CALL IDENTIFIER actualpars
^^^^^^^^^^
gram.y:155.22-34: warning: nonterminal useless in grammar: actualparlist [-Wother]
| '('actualparlist')'
^^^^^^^^^^^^^
gram.y:158.19-31: warning: nonterminal useless in grammar: actualparitem [-Wother]
: actualparitem
^^^^^^^^^^^^^
gram.y:120.26-34: warning: nonterminal useless in grammar: condition [-Wother]
: IF '(' condition')' brack_or_stat elsepart
^^^^^^^^^
gram.y:166.28-38: warning: nonterminal useless in grammar: or_boolterm [-Wother]
: boolterm or_boolterm
^^^^^^^^^^^
gram.y:166.19-26: warning: nonterminal useless in grammar: boolterm [-Wother]
: boolterm or_boolterm
^^^^^^^^
gram.y:173.30-43: warning: nonterminal useless in grammar: and_boolfactor [-Wother]
: boolfactor and_boolfactor
^^^^^^^^^^^^^^
gram.y:173.19-28: warning: nonterminal useless in grammar: boolfactor [-Wother]
: boolfactor and_boolfactor
^^^^^^^^^^
gram.y:145.30-39: warning: nonterminal useless in grammar: expression [-Wother]
: RETURN '(' expression ')'
^^^^^^^^^^
gram.y:185.38-50: warning: nonterminal useless in grammar: add_oper_term [-Wother]
: optional_sign term add_oper_term
^^^^^^^^^^^^^
gram.y:185.33-36: warning: nonterminal useless in grammar: term [-Wother]
: optional_sign term add_oper_term
^^^^
gram.y:192.26-40: warning: nonterminal useless in grammar: mul_oper_factor [-Wother]
: factor mul_oper_factor
^^^^^^^^^^^^^^^
gram.y:192.19-24: warning: nonterminal useless in grammar: factor [-Wother]
: factor mul_oper_factor
^^^^^^
gram.y:201.30-35: warning: nonterminal useless in grammar: idtail [-Wother]
| IDENTIFIER idtail
^^^^^^
gram.y:182.30-44: warning: nonterminal useless in grammar: relational_oper [-Wother]
| expression relational_oper expression
^^^^^^^^^^^^^^^
gram.y:188.19-26: warning: nonterminal useless in grammar: add_oper [-Wother]
: add_oper term
^^^^^^^^
gram.y:195.19-26: warning: nonterminal useless in grammar: mul_oper [-Wother]
: mul_oper factor mul_oper_factor
^^^^^^^^
gram.y:185.19-31: warning: nonterminal useless in grammar: optional_sign [-Wother]
: optional_sign term add_oper_term
^^^^^^^^^^^^^
gram.y:43.19-42: warning: rule useless in grammar [-Wother]
| PROGRAM IDENTIFIER block
^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:47.19-59: warning: rule useless in grammar [-Wother]
: "{" declarations subprograms sequence "}"
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:50.19-24: warning: rule useless in grammar [-Wother]
: %empty
^^^^^^
gram.y:51.19-44: warning: rule useless in grammar [-Wother]
| DECLARE varlist ENDDECLARE
^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:54.19-24: warning: rule useless in grammar [-Wother]
: %empty
^^^^^^
gram.y:55.19-45: warning: rule useless in grammar [-Wother]
| assignment_stat identifier2
^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:58.19-37: warning: rule useless in grammar [-Wother]
identifier2 : ',' assignment_stat
^^^^^^^^^^^^^^^^^^^
gram.y:59.19-37: warning: rule useless in grammar [-Wother]
| ',' assignment_stat
^^^^^^^^^^^^^^^^^^^
gram.y:63.19-22: warning: rule useless in grammar [-Wother]
: func
^^^^
gram.y:64.19-33: warning: rule useless in grammar [-Wother]
| subprograms ','
^^^^^^^^^^^^^^^
gram.y:67.19-47: warning: rule useless in grammar [-Wother]
: PROCEDURE IDENTIFIER funcbody
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:68.19-46: warning: rule useless in grammar [-Wother]
| FUNCTION IDENTIFIER funcbody
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:71.19-34: warning: rule useless in grammar [-Wother]
: formalpars block
^^^^^^^^^^^^^^^^
gram.y:74.19-24: warning: rule useless in grammar [-Wother]
: '('')'
^^^^^^
gram.y:75.19-39: warning: rule useless in grammar [-Wother]
| '(' formalparlist ')'
^^^^^^^^^^^^^^^^^^^^^
gram.y:79.19-31: warning: rule useless in grammar [-Wother]
: formalparitem
^^^^^^^^^^^^^
gram.y:80.19-35: warning: rule useless in grammar [-Wother]
| formalparlist ','
^^^^^^^^^^^^^^^^^
gram.y:84.19-31: warning: rule useless in grammar [-Wother]
: IN IDENTIFIER
^^^^^^^^^^^^^
gram.y:85.19-34: warning: rule useless in grammar [-Wother]
| INOUT IDENTIFIER
^^^^^^^^^^^^^^^^
gram.y:88.19-46: warning: rule useless in grammar [-Wother]
: statement statement_sequence
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:91.19-30: warning: rule useless in grammar [-Wother]
: ";"statement
^^^^^^^^^^^^
gram.y:92.19-50: warning: rule useless in grammar [-Wother]
| ';' statement statement_sequence
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:95.19-34: warning: rule useless in grammar [-Wother]
: '{' sequence '}'
^^^^^^^^^^^^^^^^
gram.y:98.19-30: warning: rule useless in grammar [-Wother]
: brackets_seq
^^^^^^^^^^^^
gram.y:99.19-27: warning: rule useless in grammar [-Wother]
| statement
^^^^^^^^^
gram.y:104.19-24: warning: rule useless in grammar [-Wother]
: %empty
^^^^^^
gram.y:105.19-33: warning: rule useless in grammar [-Wother]
| assignment_stat
^^^^^^^^^^^^^^^
gram.y:106.19-25: warning: rule useless in grammar [-Wother]
| if_stat
^^^^^^^
gram.y:107.19-31: warning: rule useless in grammar [-Wother]
| do_while_stat
^^^^^^^^^^^^^
gram.y:108.19-28: warning: rule useless in grammar [-Wother]
| while_stat
^^^^^^^^^^
gram.y:109.19-29: warning: rule useless in grammar [-Wother]
| select_stat
^^^^^^^^^^^
gram.y:110.19-27: warning: rule useless in grammar [-Wother]
| exit_stat
^^^^^^^^^
gram.y:111.19-29: warning: rule useless in grammar [-Wother]
| return_stat
^^^^^^^^^^^
gram.y:112.19-28: warning: rule useless in grammar [-Wother]
| print_stat
^^^^^^^^^^
gram.y:113.19-27: warning: rule useless in grammar [-Wother]
| call_stat
^^^^^^^^^
gram.y:116.19-45: warning: rule useless in grammar [-Wother]
: IDENTIFIER EXACT IDENTIFIER
^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:120.19-60: warning: rule useless in grammar [-Wother]
: IF '(' condition')' brack_or_stat elsepart
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:123.19-24: warning: rule useless in grammar [-Wother]
: %empty
^^^^^^
gram.y:124.19-36: warning: rule useless in grammar [-Wother]
| ELSE brack_or_stat
^^^^^^^^^^^^^^^^^^
gram.y:127.19-54: warning: rule useless in grammar [-Wother]
: WHILE '(' condition')' brack_or_stat
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:130.19-132.42: warning: rule useless in grammar [-Wother]
: SELECT'(' IDENTIFIER')'
^^^^^^^^^
gram.y:135.19-52: warning: rule useless in grammar [-Wother]
: DECIMAL_CONSTANT ':' brack_or_stat
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:136.19-25: warning: rule useless in grammar [-Wother]
| dec ','
^^^^^^^
gram.y:139.19-58: warning: rule useless in grammar [-Wother]
: DO brack_or_stat WHILE '(' condition ')'
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:142.19-22: warning: rule useless in grammar [-Wother]
: EXIT
^^^^
gram.y:145.19-43: warning: rule useless in grammar [-Wother]
: RETURN '(' expression ')'
^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:148.19-41: warning: rule useless in grammar [-Wother]
: PRINT '('expression ')'
^^^^^^^^^^^^^^^^^^^^^^^
gram.y:151.19-44: warning: rule useless in grammar [-Wother]
: CALL IDENTIFIER actualpars
^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:154.19-24: warning: rule useless in grammar [-Wother]
: '('')'
^^^^^^
gram.y:155.19-37: warning: rule useless in grammar [-Wother]
| '('actualparlist')'
^^^^^^^^^^^^^^^^^^^
gram.y:158.19-31: warning: rule useless in grammar [-Wother]
: actualparitem
^^^^^^^^^^^^^
gram.y:159.19-35: warning: rule useless in grammar [-Wother]
| actualparlist ','
^^^^^^^^^^^^^^^^^
gram.y:162.19-31: warning: rule useless in grammar [-Wother]
: IN expression
^^^^^^^^^^^^^
gram.y:163.19-34: warning: rule useless in grammar [-Wother]
| INOUT IDENTIFIER
^^^^^^^^^^^^^^^^
gram.y:166.19-38: warning: rule useless in grammar [-Wother]
: boolterm or_boolterm
^^^^^^^^^^^^^^^^^^^^
gram.y:169.19-29: warning: rule useless in grammar [-Wother]
: OR boolterm
^^^^^^^^^^^
gram.y:170.19-41: warning: rule useless in grammar [-Wother]
| OR boolterm or_boolterm
^^^^^^^^^^^^^^^^^^^^^^^
gram.y:173.19-43: warning: rule useless in grammar [-Wother]
: boolfactor and_boolfactor
^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:176.19-32: warning: rule useless in grammar [-Wother]
: AND boolfactor
^^^^^^^^^^^^^^
gram.y:177.19-47: warning: rule useless in grammar [-Wother]
| AND boolfactor and_boolfactor
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:180.19-39: warning: rule useless in grammar [-Wother]
: NOT '[' condition ']'
^^^^^^^^^^^^^^^^^^^^^
gram.y:181.19-35: warning: rule useless in grammar [-Wother]
| '[' condition ']'
^^^^^^^^^^^^^^^^^
gram.y:182.19-55: warning: rule useless in grammar [-Wother]
| expression relational_oper expression
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:185.19-50: warning: rule useless in grammar [-Wother]
: optional_sign term add_oper_term
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:188.19-31: warning: rule useless in grammar [-Wother]
: add_oper term
^^^^^^^^^^^^^
gram.y:189.19-45: warning: rule useless in grammar [-Wother]
| add_oper term add_oper_term
^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:192.19-40: warning: rule useless in grammar [-Wother]
: factor mul_oper_factor
^^^^^^^^^^^^^^^^^^^^^^
gram.y:195.19-49: warning: rule useless in grammar [-Wother]
: mul_oper factor mul_oper_factor
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gram.y:196.19-33: warning: rule useless in grammar [-Wother]
| mul_oper factor
^^^^^^^^^^^^^^^
gram.y:199.19-34: warning: rule useless in grammar [-Wother]
: DECIMAL_CONSTANT
^^^^^^^^^^^^^^^^
gram.y:200.19-28: warning: rule useless in grammar [-Wother]
| expression
^^^^^^^^^^
gram.y:201.19-35: warning: rule useless in grammar [-Wother]
| IDENTIFIER idtail
^^^^^^^^^^^^^^^^^
gram.y:204.19-24: warning: rule useless in grammar [-Wother]
: %empty
^^^^^^
gram.y:205.19-28: warning: rule useless in grammar [-Wother]
| actualpars
^^^^^^^^^^
gram.y:208.19-21: warning: rule useless in grammar [-Wother]
: '='
^^^
gram.y:209.19-21: warning: rule useless in grammar [-Wother]
| '<'
^^^
gram.y:210.19-22: warning: rule useless in grammar [-Wother]
| "<="
^^^^
gram.y:211.19-22: warning: rule useless in grammar [-Wother]
| "<>"
^^^^
gram.y:212.19-22: warning: rule useless in grammar [-Wother]
| ">="
^^^^
gram.y:213.19-21: warning: rule useless in grammar [-Wother]
| '>'
^^^
gram.y:216.19-21: warning: rule useless in grammar [-Wother]
: '+'
^^^
gram.y:217.19-21: warning: rule useless in grammar [-Wother]
| '-'
^^^
gram.y:220.19-21: warning: rule useless in grammar [-Wother]
: '*'
^^^
gram.y:221.19-21: warning: rule useless in grammar [-Wother]
| '/'
^^^
gram.y:224.19-26: warning: rule useless in grammar [-Wother]
: add_oper
^^^^^^^^
gram.y:225.19-24: warning: rule useless in grammar [-Wother]
| %empty
^^^^^^
能幫我嗎？
1 個解決方案
解決方案1
2 已采納 2017-05-01 03:35:53
問題是您生產的subprograms 。
但是，這對於您（以及可能偶然發現此問題和答案的任何同學）了解如何自行發現此類問題可能更有用。
StackOverflow鼓勵您提供一個“最小，完整和可驗證的示例”（MCVE） ，您應該花一點時間閱讀該幫助頁面。 要求不是因為我們喜歡讓有疑問的人生活困難。 這是因為將問題減少到最低程度是調試的關鍵部分，並且您會發現，隨着習慣的發展，發現問題的能力越來越強。 當然，由於它消除了所有不相關的噪音，它還可以幫助嘗試解決問題的任何人。
但是MCVE不僅很小。 它也是完整的 ：也就是說，這實際上是一個問題的摘錄。 僅僅說“我認為問題就在這里，所以我將僅演示這一部分”是不夠的。 您必須通過創建最少的示例並證明確實會產生相同的問題，來證明問題出在哪里。
實際上，如果您牢記這一策略，則將以不同的方式編寫程序。 您無需編寫一千行代碼，然后將其全部輸入到編譯器中，而是將編寫一些獨立的部分並檢查每個部分，然后再將它們組合為一個整體。 這樣，當您無法解決特定問題時，就已經擁有MCVE。
語法令人討厭地相互聯系，並且不像人們所希望的程序那樣模塊化。 一個生產中的少量更改會產生移位減少沖突，涉及另一個看似完全無關的生產。 但是，您通常可以將語法分成或多或少的獨立部分。 例如，您可以僅從定義表達式的語法部分開始：
%token PROGRAM
%token IDENTIFIER
%token DECIMAL_CONSTANT
%token DECLARE ENDDECLARE
%token AND CALL DEFAULT
%token FUNCTION PROCEDURE IN INOUT
%token IF ELSE DO WHILE FOR OR NOT SELECT
%token RETURN EXIT PRINT
%token EQ_LT EQ_GT NE EXACT
%left '+' '-'
%right '*' '/'
%%
expression
: optional_sign term add_oper_term
;
add_oper_term
: add_oper term
| add_oper term add_oper_term
;
term
: factor mul_oper_factor
;
mul_oper_factor
: mul_oper factor
| mul_oper factor mul_oper_factor
;
factor
: DECIMAL_CONSTANT
| expression
| IDENTIFIER idtail
;
idtail
: %empty
| actualpars
;
add_oper
: '+'
| '-'
;
mul_oper
: '*'
| '/'
;
optional_sign
: add_oper
| %empty
;
actualpars
: '('')'
| '('actualparlist')'
;
actualparlist
: actualparitem
| actualparlist ','
;
actualparitem
: IN expression
| INOUT IDENTIFIER
;
這就產生了許多移位/減少沖突，您將必須解決這些沖突，但是卻沒有任何無用的產生。 （請注意，我將所有%token聲明留在了適當的位置，因此上述內容並不是很簡單。Bison不在乎是否聲明了您從未使用過的終端，因此將聲明保留在以后的步驟中會更容易）
向上移動一步，我們可以添加condition ，其中涉及添加：
condition
: boolterm or_boolterm
;
or_boolterm
: OR boolterm
| OR boolterm or_boolterm
;
boolterm
: boolfactor and_boolfactor
;
and_boolfactor
: AND boolfactor
| AND boolfactor and_boolfactor
;
boolfactor
: NOT '[' condition ']'
| '[' condition ']'
| expression relational_oper expression
;
relational_oper
: '='
| '<'
| "<="
| "<>"
| ">="
| '>'
;
現在有更多的移位/減少沖突，但仍然沒有無用的非終結符。
下一步將添加語句產生。 在這里，我們會發現許多語句使用了非終結brack_or_stat ，它的定義如下：
brack_or_stat
: brackets_seq
| statement
;
為了避免再次處理brackets_seq ，我們可以將其臨時添加到終端列表中。 （這是隱藏語法細節的標准技術。）稍后，當我們包含brackets_seq ，我們可以刪除%token聲明。）因此，我們現在添加
%token brackets_seq
before the `%%`, and the statement productions after it:
brack_or_stat
: brackets_seq
| statement
;
statement
: %empty
| assignment_stat
| if_stat
| do_while_stat
| while_stat
| select_stat
| exit_stat
| return_stat
| print_stat
| call_stat
;
assignment_stat
: IDENTIFIER EXACT IDENTIFIER
;
if_stat
: IF '(' condition')' brack_or_stat elsepart
;
elsepart
: %empty
| ELSE brack_or_stat
;
while_stat
: WHILE '(' condition')' brack_or_stat
;
select_stat
: SELECT'(' IDENTIFIER')'
dec
DEFAULT":" brack_or_stat
;
dec
: DECIMAL_CONSTANT ':' brack_or_stat
| dec ','
;
do_while_stat
: DO brack_or_stat WHILE '(' condition ')'
;
exit_stat
: EXIT
;
return_stat
: RETURN '(' expression ')'
;
print_stat
: PRINT '('expression ')'
;
call_stat
: CALL IDENTIFIER actualpars
;
現在有更多的移位/減少沖突，但是沒有無用的非終結符。
因此，現在我們已經研究了一半以上的語法，並且有把握地確信問題不在我們所研究的部分中。 （盡管還有很多其他問題需要解決。）
因此，如果我們假設該statement還可以，那么將其設為終端，然后從測試中刪除該引用以及它引用的所有非終端。 這給我們留下了一個簡單得多的程序：（當我復制並粘貼此摘錄並通過野牛運行時，它通知我未定義assignment_stat 。因此，我將其添加到%token聲明中。）
%token PROGRAM
%token IDENTIFIER
%token DECIMAL_CONSTANT
%token DECLARE ENDDECLARE
%token AND CALL DEFAULT
%token FUNCTION PROCEDURE IN INOUT
%token IF ELSE DO WHILE FOR OR NOT SELECT
%token RETURN EXIT PRINT
%token EQ_LT EQ_GT NE EXACT
%token statement assignment_stat
%start program
%%
program
: %empty
| PROGRAM IDENTIFIER block
;
block
: "{" declarations subprograms sequence "}"
;
declarations
: %empty
| DECLARE varlist ENDDECLARE
;
varlist
: %empty
| assignment_stat identifier2
;
identifier2 : ',' assignment_stat
| ',' assignment_stat
;
subprograms
: func
| subprograms ','
;
func
: PROCEDURE IDENTIFIER funcbody
| FUNCTION IDENTIFIER funcbody
;
funcbody
: formalpars block
;
formalpars
: '('')'
| '(' formalparlist ')'
;
formalparlist
: formalparitem
| formalparlist ','
;
formalparitem
: IN IDENTIFIER
| INOUT IDENTIFIER
;
sequence
: statement statement_sequence
;
statement_sequence
: ";"statement
| ';' statement statement_sequence
;
brackets_seq
: '{' sequence '}'
;
brack_or_stat
: brackets_seq
| statement
;
現在，我們有一個充滿“無用的非終端”警告的屏幕。
但是，語法現在要簡單得多。 （如果看起來不夠簡單，則可以繼續進行簡化操作。例如，一種可能性是分離聲明。）確實，問題可能很明顯：
subprograms
: func
| subprograms ','
func : PROCEDURE IDENTIFIER funcbody
| FUNCTION IDENTIFIER funcbody
funcbody: formalpars block
block: "{" declarations subprograms sequence "}"
注意這里發生了什么： subprograms有兩個生成。 第二個顯然是遞歸的。 但是，只需花很少的工作就可以看到另一個也是遞歸的： func有兩個產品，但是都使用funcbody 。 funcbody的唯一產品使用block ，而block使用subprograms 。
因此， subprograms沒有非遞歸產生，因此它永遠不會脫離遞歸。 而且func ， funcbody或block都不能。
但是，如果block無法生成任何語句，則program的第二個產生式（ PROGRAM IDENTIFIER block ）也無法生成任何語句，從而使program: %empty成為起始符號的唯一有效產生。 這使空字符串成為唯一有效的program ，因此，野牛將所有其他非終端標記為無用。
現在，讓我們回到subprograms （正如我剛開始所說的那樣，這是當前的問題）。 定義是：
subprograms
: func
| subprograms ','
現在，這是一個非常奇怪的定義（我認為，整個語法中都會重復出現這種奇怪的現象）。 這是在說什么 該subprograms是一個func或一個subprograms后跟一個逗號。 因此它將產生：
func
func ,
func , ,
func , , ,
func , , , ,
等等。 單個func ，后跟零個或多個逗號。 它必須具有一個func，而不能具有更多。
它不能為空的事實是無限遞歸的原因。 block必須包含一個subprograms ，並且一個subprograms必須包含一個func 。 但func必須包含一個block 。 從那個旋轉木馬也無法逃脫。
因此，這里存在兩個問題： subprograms不能為空，也不能包含多個func 。 您可能正在尋找的是：
function_list: func
| function_list ',' func
subprograms : %empty
| function_list
請注意， function_list使用左遞歸。 那是故意的。 野牛產生LR解析器，它喜歡左遞歸。
如果您以前學習過LL解析器，卻以某種方式使它陷入困境，那么左遞歸就是邪惡的， 那就不要上那課了 。 LL解析器無法處理左遞歸，但是LR解析器可以處理左遞歸和右遞歸，並且可以更好地處理左遞歸（因為它不會耗盡解析器堆棧）。
為什么在這種野牛語法中會收到這么多“無用的規則/令牌”警告？
[英]Why do I get so many 'useless rule/token' warnings in this bison grammar?
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