How to handle escape sequences in string literals in ANTLR 3?

Question

I've been looking through the ANTLR v3 documentation (and my trusty copy of "The Definitive ANTLR reference"), and I can't seem to find a clean way to implement escape sequences in string literals (I'm currently using the Java target). I had hoped to be able to do something like:

fragment  ESCAPE_SEQUENCE     : '\\' '\'' { setText("'"); }     ;  STRING       : '\'' (ESCAPE_SEQUENCE | ~('\'' | '\\'))* '\''       {          // strip the quotes from the resulting token         setText(getText().substring(1, getText().length() - 1));       }      ; 

For example, I would want the input token "'Foo\'s House'" to become the String "Foo's House".

Unfortunately, the setText(...) call in the ESCAPE_SEQUENCE fragment sets the text for the entire STRING token, which is obviously not what I want.

Is there a way to implement this grammar without adding a method to go back through the resulting string and manually replace escape sequences (e.g., with something like setText(escapeString(getText())) in the STRING rule)?

Answer 1

Here is how I accomplished this in the JSON parser I wrote.

STRING       @init{StringBuilder lBuf = new StringBuilder();}     :               '"'             ( escaped=ESC {lBuf.append(getText());} |               normal=~('"'|'\\'|'\n'|'\r')     {lBuf.appendCodePoint(normal);} )*             '"'                 {setText(lBuf.toString());}     ;  fragment ESC     :   '\\'         (   'n'    {setText("\n");}         |   'r'    {setText("\r");}         |   't'    {setText("\t");}         |   'b'    {setText("\b");}         |   'f'    {setText("\f");}         |   '"'    {setText("\"");}         |   '\''   {setText("\'");}         |   '/'    {setText("/");}         |   '\\'   {setText("\\");}         |   ('u')+ i=HEX_DIGIT j=HEX_DIGIT k=HEX_DIGIT l=HEX_DIGIT                    {setText(ParserUtil.hexToChar(i.getText(),j.getText(),                                                  k.getText(),l.getText()));}          )     ;