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