[antlr-interest] The NOT (~) Operator

[Sven Busse]

Hi,

i have a problem with a grammar error message, i don't understand.
I have this grammar (reduced to the relevant bit):

grammar simpletest;

INDENTATION
	:	TAB* ~NEWLINE;

NEWLINE
	:	'\r'? '\n';

fragment
TAB	:	'\t';

Checking the grammar with ANTLRWorks gives me this error:

simpletest.g:0:0: syntax error: buildnfa: <AST>:6:11: unexpected AST node: ?

The problem seems to relate to the "~NEWLINE", because if i delete it, i
get no error. Also, if i change the "INDENTATION" to a parser rule
"indentation", i get no error, but that is not an option for me.

Can someone explain to me, what the reason behind this error is?

Thank you
Sven