<STRING> "\\\\" => (addString "\\" ; lex() );
<STRING> "\\n" => (addString "\n" ; lex() );
+<STRING> "\\r" => (addString "\r" ; lex() );
<STRING> "\\t" => (addString "\t" ; lex() );
<STRING> "\\\"" => (addString "\t" ; lex() );
<STRING> "\\". => (ErrorMsg.error (ParseState.ext (yypos,yypos))