Special character handling in ANTLR lexer - antlr

Question

I wrote the following grammar for string variable declaration. Strings are defined like anything between single quotes, but there must be a way to add a single quote to the string value by escaping using $ letter.
grammar test;
options
{
language = Java;
}
tokens
{
VAR = 'VAR';
END_VAR = 'END_VAR';
}
var_declaration: VAR string_type_declaration END_VAR EOF;
string_type_declaration: identifier ':=' string;
identifier: ID;
string: STRING_VALUE;
STRING_VALUE: '\'' ('$\''|.)* '\'';
ID: LETTER+;
WSFULL:(' ') {$channel=HIDDEN;};
fragment LETTER: (('a'..'z') | ('A'..'Z'));
This grammar doesn't work, if you try to run this code for var_declaration rule:
VAR A :='$12.2' END_VAR
I get MismatchedTokenException.
But this code works fine for string_type_declaration rule:
A :='$12.2'

Answer 1

Your STRING_VALUE isn't properly tokenized. Inside the loop ( ... )*, the $ expects a single quote after it, but the string in your input, '$12.2', doesn't have a quote after $. You should make the single quote optional ('$' '\''? | .)*. But now your alternative in the loop, the ., will also match a single quote: better let it match anything other than a single quote and $:
STRING_VALUE
: '\'' ( '$' '\''? | ~('$' | '\'') )* '\''
;
resulting in the following parse tree: