Question

Cymbol.g4来自“权威的ANTLR 4参考”。我编译并用文件t.cymbol对其进行测试。我认为应该在第2行中报告意外字符's'的错误。但是结果是该行之后的所有内容都将被忽略，而不会出现任何错误消息。谢谢！

grun Cymbol file -trace t.cymbol

enter   file, LT(1)=int
enter   varDecl, LT(1)=int
enter   type, LT(1)=int
consume [@0,14:16='int',<4>,2:0] rule type
exit    type, LT(1)=g
consume [@1,18:18='g',<23>,2:4] rule varDecl
consume [@2,19:19='=',<1>,2:5] rule varDecl
enter   expr, LT(1)=9
consume [@3,20:20='9',<24>,2:6] rule expr
exit    expr, LT(1)=;
consume [@4,21:21=';',<2>,2:7] rule varDecl
exit    varDecl, LT(1)=s
exit    file, LT(1)=s

解析器在包含“ s”时退出。解析器为什么不使用此令牌并重新同步？

Cymbol.g4

grammar Cymbol;

file:   (functionDecl | varDecl)+ ;

varDecl: type ID ('=' expr)? ';' ;

type:   'float' | 'int' | 'void' ;

functionDecl: type ID '(' formalParameters? ')' block;

formalParameters: formalParameter (',' formalParameter)*;

formalParameter: type ID;

block: '{' stat* '}';

stat: block
    | varDecl
    | 'if' expr 'then' stat ('else' stat)?
    | 'return' expr? ';'
    | expr '=' expr ';'
    | expr ';'
    ;

expr: ID '(' exprList? ')'      #Call
    | expr '[' expr ']'         #Index
    | '-' expr                  #Negate
    | '!' expr                  #Not
    | expr ('*'|'/') expr       #MultDiv
    | expr ('+'|'-') expr       #AddSub
    | expr '==' expr            #Equal
    | ID                        #Var
    | INT                       #Int
    | FLOAT                     #Float
    | '(' expr ')'              #Parens
    ;

exprList: expr (',' expr)* ;

ID: (LETTER|'_') (LETTER|DIGITAL|'_')* ;
fragment LETTER: [a-zA-Z];
fragment DIGITAL: [0-9];

INT: DIGITAL+;
FLOAT: DIGITAL+ '.' DIGITAL*
    | '.' DIGITAL+ ;

WS: [ \t\r\n]+ ->skip;
LINE_COMMENT: '//' .*? '\n' -> skip;
COMMENT: '/*' .*? '*/' ->skip;

t.cymbol

//Cymbol test
int g=9; s
float h=1.2;
int fact(int x)
{
    int z=4;
    if x==0 then return 1;
    return x * factor(x-1);
}

为什么antlr4解析器退出而没有任何错误？

0 个答案: