<$?>

(<$?>) :: Stream s Identity tok => (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b
parsec Text.Parsec.Perm, parsec Text.ParserCombinators.Parsec.Perm
The expression f <$?> (x,p) creates a fresh permutation parser consisting of parser p. The the final result of the permutation parser is the function f applied to the return value of p. The parser p is optional - if it can not be applied, the default value x will be used instead.