How to match a fixed number of characters in ANTLR 3?

I want to parse ISO 8601 dates in my ANTLR grammar.

2001-05-03

I have the following entries in my grammar file:

date    : FOUR_DIGIT ('-')? TWO_DIGIT ('-')? TWO_DIGIT ;

FOUR_DIGIT
    : TWO_DIGIT TWO_DIGIT ; 

TWO_DIGIT
    : DIGIT DIGIT ;

DIGIT   : ('0'..'9') ;

I know I can 开发者_C百科match one or more with DIGIT+ and zero or more with DIGIT*

While this works, is there a simpler syntax to specify I want to match exactly 2 DIGIT?

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Jarrod Roberson wrote:

While this works, is there a simpler syntax to specify I want to match exactly 2 DIGIT?

No, DIGIT DIGIT is the only way to match exactly two digits. ANTLR does not support something like DIGIT{2}, unfortunately.

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I'm pretty sure ANTLR 3 has no quantifiers besides *, + and ?. DIGIT DIGIT DIGIT DIGIT seems like the most reasonable way to get the behavior you want.

See http://www.antlr.org/wiki/display/ANTLR3/Grammars