问题
I am not so familiar with antlr. I am using version 4 and I have a grammar where whitespace is not important in some parts (but it might be in others, or rather its luck).
So say we have the following grammar
grammar Foo;
program : A* ;
A : ID '@' ID '(' IDList ')' ';' ;
ID : [a-zA-Z]+ ;
IDList : ID (',' IDList)* ;
WS : [ \t\r\n]+ -> skip ;
and a test input
foo@bar(X,Y);
foo@baz ( z,Z) ;
The first line is parsed correctly whereas the second one is not. I don't want to polute my rules with the places where whitespace is not relevant, since my actual grammar is more complicated than the toy example. In case it's not clear the part ID'@'ID should not have a whitespace. Whitespace in any other position shouldn't matter at all.
回答1:
Define ID '@' ID as lexer token rather than as parser token.
A : AID '(' IDList ')' ';' ;
AID : [a-zA-Z]+ '@' [a-zA-Z]+;
Other options
- enable/disable whitespaces in your token stream, e.g. here
- enable/disable whitespaces with lexer modes (may be a problem because lexer modes are triggered on context, which is not easy to determine in your case)
回答2:
Even though you are skipping WS, lexer rules are still sensitive to the existence of the whitespace characters. Skip simply means that no token is generated for consumption by the parser. Thus, the lexer Addr rule explicitly does not permit any interior whitespace characters.
Conversely, the a and idList parser rules never see interior whitespace tokens so those rules are insensitive to the occurrence of whitespace characters occurring between the generated tokens.
grammar Foo;
program : a* EOF ; // EOF will require parsing the entire input
a : Addr LParen IDList RParen Semi ;
idList : ID (Comma ID)* ; // simpler equivalent construct
Addr : ID '@' ID
ID : [a-zA-Z]+ ;
WS : [ \t\r\n]+ -> skip ;
来源：https://stackoverflow.com/questions/29524952/ignoring-whitespace-in-certain-parts-in-antlr4