/**
* Returns a parser that produces a digit (0 to 9).
*
* @param missing The error if there is no character on the stream to produce a digit with.
* @param sat The error if the produced character is not a digit.
* @return A parser that produces a digit (0 to 9).
*/
public static <E> Parser<Stream<Character>, Digit, E> digit(
final F0<E> missing, final F<Character, E> sat) {
return StreamParser.satisfy(missing, sat, c -> Character.isDigit(c))
.map(c1 -> Digit.fromChar(c1).some());
}
