Question

我试图弄清楚为什么我的Antlr生成的解析器无法将输入的一部分识别为与我的一条规则（“ and_converge”规则，“网关”的一部分）匹配。我的语法如下：

process           :   PROCESS id CURLY_OPEN (stmt_list | pool_list) CURLY_CLOSE EOF ; /* starting rule */
stmt_list         :   (stmt STMT_TERM?)* ;
stmt              :   sequence | sequence_elem | association ;
sequence          :   sequence_elem sequence_flow sequence_elem (sequence_flow sequence_elem)* ;
sequence_elem     :   activity | gateway | event | link ;
activity          :   task | subprocess ;
task              :   SQRE_OPEN task_type id
                      (VERT_LINE (input_set)? (output_set)?)?   /* input/output sets */
                      (VERT_LINE attr_list)?                    /* attributes for activity */
                      (VERT_LINE boundary_event)*               /* associated boundary events */
                      SQRE_CLOSE ;
task_type         :   USER | SERVICE | SCRIPT ;
event             :   PAREN_OPEN event_type id (VERT_LINE attr_list)? PAREN_CLOSE ;
gateway           :   ANGLE_OPEN (fork_diverge | condition_diverge | event_diverge | and_converge | or_converge) ANGLE_CLOSE ;
fork_diverge      :   FORK id (VERT_LINE attr_list)? VERT_LINE outflows ;
event_diverge     :   EVENT_SPLIT VERT_LINE event_links ;
condition_diverge :   (OR_SPLIT | XOR_SPLIT) id (VERT_LINE attr_list)? VERT_LINE cond_outflows ;
and_converge      :   JOIN id (VERT_LINE attr_list)? (VERT_LINE inflows)? ;
or_converge       :   (XOR_JOIN | OR_JOIN) id (VERT_LINE attr_list)? (VERT_LINE inflows)? ;
inflows           :   IN ':' link_list ;
outflows          :   OUT ':' link_list ;
cond_outflows     :   OUT ':' cond_outflow (',' cond_outflow)* (DEFAULT ':' link)?;
cond_outflow      :   expression ':' link ;

为了简洁起见，我省略了大部分语法，但是您可以在此处看到完整版本：https://github.com/bspies/dotbpm/blob/dotbpm-parser/src/main/java/dot/bpm/parser/antlr/DOTBPM.g4。

当我在语法中输入以下内容时，它将失败：

/* A fork followed by a join, 4 "sequences" altogether */
process fork_join {
   (> start) ==> [user t1] ==>
   <fork g1 | out: #[t2], #[t3]>
   [user t2] ==> #<g2>
   [user t3] ==> #<g2>
   <join g2> ==> (/ end)
}

它在与“加入”网关：line 7:4 no viable alternative at input '<join'的行上失败。对其进行调试，似乎无法遵循“ stmt”规则，无法确定采用哪种替代方法。考虑到执行它的“ fork”规则工作得很好，并且在语法上（即通过“ gateway”规则）采用了非常相似的路径，因此这令人感到困惑。

解析树在这里：

Answer 1

如果运行此代码：

String source = "/* A fork followed by a join, 4 \"sequences\" altogether */\n" +
        "process fork_join {\n" +
        "   (> start) ==> [user t1] ==>\n" +
        "   <fork g1 | out: #[t2], #[t3]>\n" +
        "   [user t2] ==> #<g2>\n" +
        "   [user t3] ==> #<g2>\n" +
        "   <join g2> ==> (/ end)\n" +
        "}";

DOTBPMLexer lexer = new DOTBPMLexer(CharStreams.fromString(source));

CommonTokenStream stream = new CommonTokenStream(lexer);
stream.fill();

for (Token t : stream.getTokens()) {
    System.out.printf("type=%-20s text=`%s`%n", DOTBPMLexer.VOCABULARY.getDisplayName(t.getType()), t.getText().replace("\n", "\\n"));
}

并检查其输出：

type=PROCESS              text=`process`
type=ID                   text=`fork_join`
type='{'                  text=`{`
type='('                  text=`(`
type='>'                  text=`>`
type=ID                   text=`start`
type=')'                  text=`)`
type='==>'                text=`==>`
type='['                  text=`[`
type=USER                 text=`user`
type=ID                   text=`t1`
type=']'                  text=`]`
type='==>'                text=`==>`
type='<'                  text=`<`
type=FORK                 text=`fork`
type=ID                   text=`g1`
type='|'                  text=`|`
type=OUT                  text=`out`
type=':'                  text=`:`
type='#'                  text=`#`
type='['                  text=`[`
type=ID                   text=`t2`
type=']'                  text=`]`
type=','                  text=`,`
type='#'                  text=`#`
type='['                  text=`[`
type=ID                   text=`t3`
type=']'                  text=`]`
type='>'                  text=`>`
type='['                  text=`[`
type=USER                 text=`user`
type=ID                   text=`t2`
type=']'                  text=`]`
type='==>'                text=`==>`
type='#'                  text=`#`
type='<'                  text=`<`
type=ID                   text=`g2`
type='>'                  text=`>`
type='['                  text=`[`
type=USER                 text=`user`
type=ID                   text=`t3`
type=']'                  text=`]`
type='==>'                text=`==>`
type='#'                  text=`#`
type='<'                  text=`<`
type=ID                   text=`g2`
type='>'                  text=`>`
type='<'                  text=`<`
type=ID                   text=`join`
type=ID                   text=`g2`
type='>'                  text=`>`
type='==>'                text=`==>`
type='('                  text=`(`
type='/'                  text=`/`
type=ID                   text=`end`
type=')'                  text=`)`
type='}'                  text=`}`
type=EOF                  text=`<EOF>`

您会看到输入join变成了ID，而不是JOIN。这就是Mike首先打印令牌的意思。

这是因为您有错字：

JOIN           :   [Jj}[Oo][Ii][Nn] ;                     /* synchronized merge (AND) */
OR_JOIN        :   [Oo][Rr]'-'[Jj}[Oo][Ii][Nn] ;          /* structured synchronized merge (OR) */
XOR_JOIN       :   [Xx][Oo][Rr]'-'[Jj}[Oo][Ii][Nn] ;      /* unsynchronized merge (XOR) */

请注意所有这些词法分析器规则中的[Jj}[Oo]，它们将匹配一个字符（J，j，}，[中的一个，O或o）。

您（最有可能）的意思是：

JOIN           :   [Jj][Oo][Ii][Nn] ;                     /* synchronized merge (AND) */
OR_JOIN        :   [Oo][Rr]'-'[Jj][Oo][Ii][Nn] ;          /* structured synchronized merge (OR) */
XOR_JOIN       :   [Xx][Oo][Rr]'-'[Jj][Oo][Ii][Nn] ;      /* unsynchronized merge (XOR) */

解析器无法从输入中识别规则

1 个答案: