Parsing 为什么这个非常简单的语法会导致GLR解析器阻塞？

我尝试过几种不同的解析器生成器（Bison、DParser等），它们声称能够生成GLR解析器，即能够处理歧义语法的解析器。下面是一个非常简单的模棱两可的语法，就是我所说的类型：

START: A | B;
A: C | D;
B: C | D;
C: T1 | T2;
D: T3 | T4;
T1: 't1';
T2: 't2';
T3: 't3';
T4: 't4';

我可以很好地生成解析器，但是当我给出应该有效的解析器输入时，会出现“未解决的歧义”错误或完全崩溃。当我将语法更改为明确的版本时，没有任何问题

我不了解GLR解析器的哪些方面？我认为重点在于，在出现歧义的情况下，所有可能的解析都会被跟踪，直到它们合并或到达死胡同。我所需要的只是一个解析器，它可以告诉我是否存在任何有效的输入解析

谢谢你的帮助

编辑：

这令人沮丧。使用%dprec和%merge，我已经能够让Bison处理不明确的规则和终端，但它仍然被我需要处理的非常简单但高度病态的伪英语语法所阻塞：

S: NP VP | NPA VP;
NPA: D N | NP PP;
NP: D N | NP PP | NPA;
VP: V NP | VP PP;
PP: P NP;
D: "the" | "a";
P: "in" | "with";
V: "saw";
N: "saw" | "girl" | "boy" | "park" | "telescope";

输入“一个男孩看到了一个女孩”，Bison无法解析并返回代码1。另一方面，Tom完美地处理了这种语法和输入句子，甚至通过将未知终端分配给所有可能的终端类型，自然地处理它们。但与Bison不同的是，Tom对大量语法感到窒息。（我所说的“扼流圈”是指以各种不同方式出现故障。如果故障模式有帮助，我可以报告这些情况。）

---

有人有其他想法吗？

不幸的是，bison确实坚持生成（单个）解析，因此您必须指定某种方法来合并不明确的解析。如果您不这样做，并且存在多个可能的解析，bison的GLR解析器确实会抱怨解析不明确

如果您真的不关心多个解析中的哪一个被接受，那么让bison服从您的意愿并不太困难。最简单的方法就是为每个可能不明确的产品分配不同的

%dprec

。然后，Bison将选择最优先的适用产品

您甚至可以通过一个简单的

%merge

函数让bison告诉您有关多个解析的信息；这本书中有一个例子。（此功能的文档不是很好，但可能足以满足您的需要。如果不是，请随时提出更具体的问题。）

我对DParser没有太多的经验，但它表明它在面对多个可能的解析时的行为是相似的：默认情况下是抱怨，但您可以提供自己的一个简单的合并函数：（引自第12节，含糊不清）

歧义会根据优先级和关联性自动解决。此外，当其他解决技术失败时，用户定义的歧义解决是可能的。默认的歧义处理程序会对未解决的歧义产生致命错误。此行为可以替换为用户定义的解析器，其签名在

dparse.h

中提供

---

下面是第二个示例的bison GLR语法示例。我遗漏了lexer，这真的不相关（而且有点尴尬，因为我赶时间）

汇编：

$ make ambig2
bison30 -v -d -o ambig2.c ambig2.y 
ambig2.y: warning: 6 shift/reduce conflicts [-Wconflicts-sr]
ambig2.y: warning: 10 reduce/reduce conflicts [-Wconflicts-rr]
gcc-4.8 -ggdb -Wall -D_POSIX_C_SOURCE=200809L -std=c99 -c -o ambig2.o ambig2.c
gcc-4.8   ambig2.o   -o ambig2
rm ambig2.o ambig2.c

示例解析：

$ ./ambig2 <<<"a boy saw a girl"
D: a
N: boy
NPA: D N
V: saw
D: a
N: girl
NPA: D N
NP: NPA
VP: V NP 
S: NPA VP
yyparse returned 0

$ ./ambig2 <<<"a saw saw the saw in a saw"
D: a
N: saw
NPA: D N
V: saw
D: the
N: saw
NPA: D N
NP: NPA
VP: V NP 
P: in
D: a
N: saw
NPA: D N
NP: NPA
PP: P NP
VP: VP PP
S: NPA VP
yyparse returned 0

---

$。/ambig2您的语法不会导致GLR解析器阻塞

您需要一个GLR解析引擎，它提供GLR解析器应该提供的内容：面对歧义进行解析，并将结果交给您。假设您使用其他上下文来解决歧义。（你可以纠结上下文检查
如果你真的坚持要避免产生上下文歧义，那么就把它引入解析过程

以下是OP问题的输出，提供给我们的DMS软件再工程工具包的GLR解析器生成器。我必须定义一个与DMS兼容的lexer和语法：

Lexer（将单个标记定义为单词；更具扩展性的版本
可能已经定义了单词类标记，例如D P V N）：

语法（DMS不需要EBNF）：

示例文件“aboysawagirl.txt”

从头到尾，构建lexer和解析器（大约10分钟的摸索…）

解析示例文件并转储自动生成的树：

C:\DMS\Domains\simpenglish\Tools\Parser\Source>run ..\domainparser ++AST ..\..\Lexer\aboysawagirl.txt
simpenglish Domain Parser Version 2.5.15
Copyright (C) 1996-2013 Semantic Designs, Inc; All Rights Reserved; SD Confidential
Powered by DMS (R) Software Reengineering Toolkit
24 tree nodes in tree.
3 ambiguity nodes in tree.
(AMBIGUITY<S=11>@simpenglish=31@#1f35140^0{2} Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
 (S@simpenglish=1@#1f350e0^1#1f35140:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
  (AMBIGUITY<NP=12>@simpenglish=31@#1f34ba0^1#1f350e0:1{2} Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   (NP@simpenglish=5@#1f34b80^1#1f34ba0:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |(D@simpenglish=12@#1f34aa0^2#1f34b80:1#1f34b40:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | ('a'@simpenglish=22@#1f349c0^1#1f34aa0:1[Keyword:0] Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'a'
   |)D#1f34aa0
   |(N@simpenglish=18@#1f34b20^2#1f34b80:2#1f34b40:2 Line 1 Column 3 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | ('boy'@simpenglish=27@#1f34a80^1#1f34b20:1[Keyword:0] Line 1 Column 3 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'boy'
   |)N#1f34b20
   )NP#1f34b80
   (NP@simpenglish=7@#1f34c60^1#1f34ba0:2 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |(NPA@simpenglish=3@#1f34b40^2#1f35040:1#1f34c60:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | (D@simpenglish=12@#1f34aa0^2... [ALREADY PRINTED] ...)
   | (N@simpenglish=18@#1f34b20^2... [ALREADY PRINTED] ...)
   |)NPA#1f34b40
   )NP#1f34c60
  )AMBIGUITY#1f34ba0
  (VP@simpenglish=8@#1f34fc0^1#1f350e0:2 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   (V@simpenglish=15@#1f34d60^1#1f34fc0:1 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |('saw'@simpenglish=25@#1f34b00^2#1f34d60:1#1f34d40:1[Keyword:0] Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'saw'
   )V#1f34d60
   (AMBIGUITY<NP=12>@simpenglish=31@#1f34f00^2#1f34f80:2#1f34fc0:2{2} Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |(NP@simpenglish=5@#1f34e60^1#1f34f00:1 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | (D@simpenglish=12@#1f34da0^2#1f34e60:1#1f34de0:1 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |  ('a'@simpenglish=22@#1f34ce0^1#1f34da0:1[Keyword:0] Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'a'
   | )D#1f34da0
   | (N@simpenglish=17@#1f34dc0^2#1f34e60:2#1f34de0:2 Line 1 Column 13 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |  ('girl'@simpenglish=26@#1f34d80^1#1f34dc0:1[Keyword:0] Line 1 Column 13 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'girl'
   | )N#1f34dc0
   |)NP#1f34e60
   |(NP@simpenglish=7@#1f34f20^1#1f34f00:2 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | (NPA@simpenglish=3@#1f34de0^1#1f34f20:1 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |  (D@simpenglish=12@#1f34da0^2... [ALREADY PRINTED] ...)
   |  (N@simpenglish=17@#1f34dc0^2... [ALREADY PRINTED] ...)
   | )NPA#1f34de0
   |)NP#1f34f20
   )AMBIGUITY#1f34f00
  )VP#1f34fc0
 )S#1f350e0
 (S@simpenglish=2@#1f35040^1#1f35140:2 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
  (NPA@simpenglish=3@#1f34b40^2... [ALREADY PRINTED] ...)
  (VP@simpenglish=8@#1f34f80^1#1f35040:2 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   (V@simpenglish=15@#1f34d40^1#1f34f80:1 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |('saw'@simpenglish=25@#1f34b00^2... [ALREADY PRINTED] ...)
   )V#1f34d40
   (AMBIGUITY<NP=12>@simpenglish=31@#1f34f00^2... [ALREADY PRINTED] ...)
  )VP#1f34f80
 )S#1f35040
)AMBIGUITY#1f35140

C:\DMS\Domains\simpenglish\Tools\Parser\Source>run..\domainparser++AST..\Lexer\aboyasawairl.txt
simpenglish域解析器版本2.5.15
版权所有（C）1996-2013语义设计公司；保留所有权利；SD机密
由DMS（R）软件再工程工具包提供支持
树中有24个树节点。
树中有3个模糊节点。
(AMBIGUITY@simpenglish=31#1f35140^0{2}行1列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
(S@simpenglish=1@#1f350e0^1#1f35140:1第1行第1列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
(AMBIGUITY@simpenglish=31@#1f34ba0^1#1f350e0:1{2}行1列1文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
(NP@simpenglish=5@#1f34b80^1#1f34ba0:1第1行第1列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
|(D@simpenglish=12@#1f34aa0^2#1f34b80:1#1f34b40:1第1行第1列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
|（'a'@simpenglish=22@#1f349c0^1#1f34aa0:1[关键字：0]第1行第1列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt）'a'
|)D#1f34aa0
|(N@simpenglish=18@#1f34b20^2#1f34b80:2#1f34b40:2第1行第3列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
|（'boy'@simpenglish=27@#1f34a80^1#1f34b20:1[Keyword:0]第1行第3列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt）'boy'
|)N#1f34b20
)NP#1f34b80
(NP@simpenglish=7@#1f34c60^1#1f34ba0:2第1行第1列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
|(NPA@simpenglish=3@#1f34b40^2#1f35040:1#1f34c60:1第1行第1列文件C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
| (D@simpenglish=1
%%
%%main
#skip "\s+"
#skip "[\u000d\u000a]+"
#token 'the' "the"
#token 'a' "a"
#token 'in' "in"
#token 'with' "with"
#token 'saw' "saw"
#token 'girl' "girl"
#token 'boy' "boy"
#token 'park' "park"
#token 'telescope' "telescope"
%%

S = NP VP ;
S = NPA VP ;
NPA = D N ;
NPA = NP PP ;
NP = D N ;
NP = NP PP ;
NP = NPA ;
VP = V NP ;
VP = VP PP ;
PP = P NP ;
D = 'the' ;
D = 'a';
P = 'in' ;
P = 'with' ;
V = 'saw' ;
N = 'saw' ;
N = 'girl' ;
N = 'boy' ;
N = 'park' ;
N = 'telescope' ;

a boy saw a girl\n

C:\DMS\Domains\simpenglish\Tools\Parser\Source>run ..\domainparser ++AST ..\..\Lexer\aboysawagirl.txt
simpenglish Domain Parser Version 2.5.15
Copyright (C) 1996-2013 Semantic Designs, Inc; All Rights Reserved; SD Confidential
Powered by DMS (R) Software Reengineering Toolkit
24 tree nodes in tree.
3 ambiguity nodes in tree.
(AMBIGUITY<S=11>@simpenglish=31@#1f35140^0{2} Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
 (S@simpenglish=1@#1f350e0^1#1f35140:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
  (AMBIGUITY<NP=12>@simpenglish=31@#1f34ba0^1#1f350e0:1{2} Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   (NP@simpenglish=5@#1f34b80^1#1f34ba0:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |(D@simpenglish=12@#1f34aa0^2#1f34b80:1#1f34b40:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | ('a'@simpenglish=22@#1f349c0^1#1f34aa0:1[Keyword:0] Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'a'
   |)D#1f34aa0
   |(N@simpenglish=18@#1f34b20^2#1f34b80:2#1f34b40:2 Line 1 Column 3 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | ('boy'@simpenglish=27@#1f34a80^1#1f34b20:1[Keyword:0] Line 1 Column 3 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'boy'
   |)N#1f34b20
   )NP#1f34b80
   (NP@simpenglish=7@#1f34c60^1#1f34ba0:2 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |(NPA@simpenglish=3@#1f34b40^2#1f35040:1#1f34c60:1 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | (D@simpenglish=12@#1f34aa0^2... [ALREADY PRINTED] ...)
   | (N@simpenglish=18@#1f34b20^2... [ALREADY PRINTED] ...)
   |)NPA#1f34b40
   )NP#1f34c60
  )AMBIGUITY#1f34ba0
  (VP@simpenglish=8@#1f34fc0^1#1f350e0:2 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   (V@simpenglish=15@#1f34d60^1#1f34fc0:1 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |('saw'@simpenglish=25@#1f34b00^2#1f34d60:1#1f34d40:1[Keyword:0] Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'saw'
   )V#1f34d60
   (AMBIGUITY<NP=12>@simpenglish=31@#1f34f00^2#1f34f80:2#1f34fc0:2{2} Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |(NP@simpenglish=5@#1f34e60^1#1f34f00:1 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | (D@simpenglish=12@#1f34da0^2#1f34e60:1#1f34de0:1 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |  ('a'@simpenglish=22@#1f34ce0^1#1f34da0:1[Keyword:0] Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'a'
   | )D#1f34da0
   | (N@simpenglish=17@#1f34dc0^2#1f34e60:2#1f34de0:2 Line 1 Column 13 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |  ('girl'@simpenglish=26@#1f34d80^1#1f34dc0:1[Keyword:0] Line 1 Column 13 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt)'girl'
   | )N#1f34dc0
   |)NP#1f34e60
   |(NP@simpenglish=7@#1f34f20^1#1f34f00:2 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   | (NPA@simpenglish=3@#1f34de0^1#1f34f20:1 Line 1 Column 11 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |  (D@simpenglish=12@#1f34da0^2... [ALREADY PRINTED] ...)
   |  (N@simpenglish=17@#1f34dc0^2... [ALREADY PRINTED] ...)
   | )NPA#1f34de0
   |)NP#1f34f20
   )AMBIGUITY#1f34f00
  )VP#1f34fc0
 )S#1f350e0
 (S@simpenglish=2@#1f35040^1#1f35140:2 Line 1 Column 1 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
  (NPA@simpenglish=3@#1f34b40^2... [ALREADY PRINTED] ...)
  (VP@simpenglish=8@#1f34f80^1#1f35040:2 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   (V@simpenglish=15@#1f34d40^1#1f34f80:1 Line 1 Column 7 File C:/DMS/Domains/simpenglish/Tools/Lexer/aboysawagirl.txt
   |('saw'@simpenglish=25@#1f34b00^2... [ALREADY PRINTED] ...)
   )V#1f34d40
   (AMBIGUITY<NP=12>@simpenglish=31@#1f34f00^2... [ALREADY PRINTED] ...)
  )VP#1f34f80
 )S#1f35040
)AMBIGUITY#1f35140