<|?>

(<|?>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b
parsec Text.Parsec.Perm, parsec Text.ParserCombinators.Parsec.Perm
The expression perm <||> (x,p) adds parser p to the permutation parser perm. The parser p is optional - if it can not be applied, the default value x will be used instead. Returns a new permutation parser that includes the optional parser p.