Question

I wrote a stub for a grammar (only matches comments so far), and it’s giving me the error:

syntax error: invalid char literal: <INVALID>

Moreover, I’ve tracked down the error to being in the following command:

... ~LINE_ENDING* ...
LINE_ENDING     : ( '\n' | '\r' | '\r\n');

Can someone help me fix this?

Answer 1

The ~ operator can only be applied to a set. In a lexer, the elements of a set are characters of an input stream. In other words, you can have this:

~(  'a'..'z'
|   'C'
|   '\r'
|   '\n'
)

But you can’t have this because it’s a sequence (of two characters) instead of a set.

~('\r\n')

The problem you encountered is an extension of this second case.