Tries 'r' on the input. If it fails, the rule succeeds, without consuming any input. If 'r' succeeds, then negLookahead!r fails. Low-level implementation of '!r'.
See Implementation
Tries 'r' on the input. If it fails, the rule succeeds, without consuming any input. If 'r' succeeds, then negLookahead!r fails. Low-level implementation of '!r'.