Some special characters allowed in C# are not allowed in boo currently, such as \a (a console beep). Add these lines to the SESC section of boo.g and booel.g: ( 'a'! {text.Length = _begin; text.Append("\a"); }) | ( 'b'! {text.Length = _begin; text.Append("\b"); }) | ( 'f'! {text.Length = _begin; text.Append("\f"); }) | ( '0'! {text.Length = _begin; text.Append("\0"); }) | I had to use that code instead of $setText because these special characters are not recognized by ANTLR's java runtime. Test with: print "here is a beep: \a" print "hello\b backspace" According to the C# specification, "\v" (vertical tab) should be allowed too: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csspec/html/vclrfcsharpspec_C.asp but I could not get it to work with ANTLR, unless I used
v instead and manually changed the string in the generated BooLexer.cs file back to \v. It is not important to me.