代码：
%{
#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
;
%%
这是我为野牛创建的语法，但是当我在终端上尝试bison gram.y时会出现一堆警告。试图改变他们写的顺序，但我仍然得到相同的东西 这是终端输出
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
^^^^^^
任何可以帮助我吗？
答案 0 :(得分：2)
问题在于您subprograms的制作。
但是对于你（以及任何可能偶然发现这个问题和答案的同学）来说，了解如何自行找到这样的问题可能更有用。
StackOverflow鼓励您提供"Minimal, Complete and Verifiable Example" (MCVE)，您应该花点时间阅读该帮助页面。请求不是因为我们喜欢让有疑问的人生活困难。这是因为将问题减少到最低限度的行为是调试的关键部分，你会发现，随着它变成一种习惯，你会越来越好地发现你的问题。当然，它也可以帮助任何人帮助你解决问题，因为它消除了所有无关的噪音。
但是MCVE不仅仅是小型的。它也是完整的：也就是说，它是一个实际展示问题的摘录。仅仅说'＃34;我认为问题就在这里是不够的，所以我只会展示这一部分。＆＃34;您必须通过创建最小示例并显示它确实存在同样的问题来实际证明问题是您认为的问题。
事实上，如果你坚持这个策略，你将以不同的方式编写你的程序。不是编写一千行代码然后将它们全部输入编译器，而是编写很少的自包含部分并在将它们组合成一个整体之前检查每个部分。这样，当您无法找出特定问题时，您已经拥有了MCVE。
语法令人烦恼地相互联系，并且几乎不像程序那样模块化。一个生产中的一点变化可以产生一个转移 - 减少冲突，涉及另一个看似完全无关的生产。尽管如此，您通常可以将语法分成或多或少的单独组件。例如，您可以从定义表达式的语法部分开始：
%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
;
这会产生一些你必须解决的转移/减少冲突，但它没有无用的产品。 （请注意，我保留了所有%token声明，因此上面的非常最小.Bison不关心你是否宣布你从未使用的终端，所以它在接下来的步骤中更容易留下声明。）
向上移动一步，我们可以添加condition，其中包括添加：
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
: '='
| '<'
| "<="
| "<>"
| ">="
| '>'
;
现在有更多的转移/减少冲突，但仍然没有无用的非终端。
下一步是添加语句产生。在这里，我们将发现许多语句使用非终端brack_or_stat，其定义为：
brack_or_stat
: brackets_seq
| statement
;
为了避免处理brackets_seq，我们可以暂时将其添加到终端列表中。 （这是隐藏语法细节的标准技术。）稍后，当我们包含brackets_seq的作品时，我们可以删除%token声明。）所以我们现在添加
%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
;
现在还有更多的转移/减少冲突，但没有无用的非终端。
所以现在我们已经查看了一半以上的语法，并且有理由相信问题不在我们看过的部分。 （虽然还有很多其他问题需要解决。）
因此，如果我们假设statement是正常的，那么让它成为一个终端，然后删除它以及它从测试中引用的所有非终端。这给我们留下了一个更简单的程序:(当我复制并粘贴此摘录并通过野牛运行时，它告诉我assignment_stat未定义。所以我只是将它添加到%token声明。）
%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
;
现在我们有一个充满了＆＃34;无用的非终端＆＃34;警告。
然而，语法现在变得更加简单。 （如果它看起来不够简单，你可以继续进行简化练习。例如，一种可能性是将声明分开。）事实上，问题可能是显而易见的：
subprograms
: func
| subprograms ','
func : PROCEDURE IDENTIFIER funcbody
| FUNCTION IDENTIFIER funcbody
funcbody: formalpars block
block: "{" declarations subprograms sequence "}"
请注意这里发生了什么：subprograms有两个作品。第二个显然是递归的。但是看到另一个也是递归的，只需要很少的工作：func有两个制作，但都使用funcbody; funcbody仅生产使用block，block使用subprograms。
所以subprograms没有非递归生成，因此它永远不会突破递归。 func，funcbody或block也不能。
但如果block无法生成任何句子，则program（PROGRAM IDENTIFIER block）的第二次制作也无法生成任何句子，只留下program: %empty作为唯一有效的作品起始符号。这使得空字符串成为唯一有效的program，因此bison将每个其他非终端标记为无用。
现在，让我们回到subprograms（正如我在开头所说，这是当前的问题）。定义是：
subprograms
: func
| subprograms ','
现在，这是一个非常奇怪的定义（而且，我认为，整个语法中都会重复这种奇怪的现象）。这是什么意思？ subprograms是func或subprograms，后跟逗号。所以它会产生：
func
func ,
func , ,
func , , ,
func , , , ,
等等。单个func，后跟零个或多个逗号。它必须有一个功能，它不能有更多功能。
它不能为空的事实是无限递归的原因。 block必须包含subprograms，而subprograms必须包含一个func。但func必须包含block。而且旋转木马没有逃脱。
所以这里有两个问题：subprograms不能为空，也不能包含多个func。您可能正在寻找的是：
function_list: func
| function_list ',' func
subprograms : %empty
| function_list
请注意function_list使用左递归。这是故意的。 Bison生成LR解析器，它喜欢左递归。
如果你以前研究过LL解析器并且以某种方式将它放到你的头脑中，那么离开递归就是邪恶的，会忘记那个教训。 LL解析器不能处理左递归，但LR解析器可以处理左右递归，并更好地处理左递归（因为它不会占用解析器堆栈）。