JFlex Lexer Configuration Issue: Unexpected Character Error

I'm working on creating a lexer for a custom configuration file format using JFlex. However, I am encountering an issue with my .flex file and receiving an "Unexpected character" error during compilation.

Here is the content of my .flex file:

%{import com.intellij.psi.TokenType;import com.intellij.psi.tree.IElementType;import static de.flox.floxsupport.FloxTypes.*;StringBuffer string = new StringBuffer();private IElementType token(int type) {    switch (type) {        case FLOX_CONFIG: return FLOX_CONFIG;        case FLOX_KEYWORD: return FLOX_KEYWORD;        case FLOX_NUMBER: return FLOX_NUMBER;        case FLOX_STRING: return FLOX_STRING;        case FLOX_SYMBOL: return FLOX_SYMBOL;        default: return TokenType.BAD_CHARACTER;    }}%}%%unicode%cup%line%columnLineTerminator = \r|\n|\r\nInputCharacter = [^\r\n]WhiteSpace     = {LineTerminator} | [ \t\f]TraditionalComment   = "/*" [^*] ~"*/" | "/*" "*"+"/"EndOfLineComment     = "//" {InputCharacter}* {LineTerminator}?Identifier = [a-zA-Z_][a-zA-Z0-9_]*DecIntegerLiteral = 0 | [1-9][0-9]*%state STRING%%/* Lexical rules *//* keywords and symbols */"@"[a-zA-Z_][a-zA-Z0-9_]* { return token(FLOX_CONFIG); }[a-zA-Z_][a-zA-Z0-9_]* { return token(FLOX_KEYWORD); }[0-9]+ { return token(FLOX_NUMBER); }\"([^"\\]|\\.)*\" { return token(FLOX_STRING); }/* single-line comments */"//".* { /* Ignore single-line comments */ }/* whitespace */\s+ { /* Ignore whitespace */ }/* symbols and punctuation */[{}:.,] { return token(FLOX_SYMBOL); }/* handle errors */. { return TokenType.BAD_CHARACTER; }<STRING> {    \" {        yybegin(YYINITIAL);        return token(FLOX_STRING, string.toString());    }    [^\n\r\"\\]+ { string.append(yytext()); }    \\t { string.append('\t'); }    \\n { string.append('\n'); }    \\r { string.append('\r'); }    \\\" { string.append('\"'); }    \\ { string.append('\\'); }}/* catch-all for unexpected characters */[^] { throw new Error("Illegal character <" + yytext() +">"); }

Error Message:

`Reading ".\\src\\main\\resources\\FloxLexer.flex"Error in file ".\\src\\main\\resources\\FloxLexer.flex" (line 33):Unexpected character"@"\[a-zA-Z\_\]\[a-zA-Z0-9\_\]\* { return token(FLOX_CONFIG); }^1 error, 0 warnings.

I attempted to use JFlex to compile a lexer definition for a custom configuration format. The .flex file includes patterns for keywords, symbols, numbers, strings, and comments, and uses JFlex-specific syntax to define how tokens are recognized and returned.

What I tried:

1. Creating the .flex File:

   • I wrote a lexer specification using JFlex syntax to match various tokens, including keywords starting with the @ symbol.

2. Running JFlex:

   • I used the JFlex tool to compile the .flex file into a Java lexer class. Specifically, I executed the command:

     java -jar /path/to/jflex.jar FloxLexer.flex

   • I replaced /path/to/jflex.jar with the actual path to the JFlex JAR file.

What I was expecting:

• I expected JFlex to successfully generate a Java lexer class from the .flex file without errors.
• The lexer should correctly recognize tokens such as keywords starting with the @ symbol, numbers, strings, and various punctuation marks, and generate the appropriate token types.