Antlr Lexer exclude a certain pattern

问题

In Antlr Lexer, How can I achieve parsing a token like this:

A word that contains any non-space letter but not '.{' inside it. Best I can come up with is using a semantics predicate.

WORD: WL+   {!getText().contains(".{")};
WL: ~[ \n\r\t];

I'm a bit worried to use semantics predicate though cause WORD here will be lexed millions of times I would think to put a semantics predicate will hit the performance.

This is coming from the requirement that I need to parse something like:

TOKEN_ONE.{TOKEN_TWO}

while TOKEN_ONE can include . and { in its letter.

I'm using Antlr 4.

回答1:

You need to limit your predicate evaluation to the case immediately following a . in the input.

WORD
  : ( ~[. \t\r\n]
    | '.' {_input.LA(1)!='{'}?
    )+
  ;

回答2:

How about rephrasing your question to the equivalent "A word contains any character except whitespace or dot or left brace-bracket."

Then the lexer rule is just:

 WORD:  ~[ \n\r\t.{]*

来源：https://stackoverflow.com/questions/19224181/antlr-lexer-exclude-a-certain-pattern