/**
* Returns a parser that produces an element from the stream if it is available and fails
* otherwise.
*
* @param e The error to fail with if no element is available.
* @return A parser that produces an element from the stream if it is available and fails
* otherwise.
*/
public static <I, E> Parser<Stream<I>, I, E> element(final F0<E> e) {
return parser(
is ->
is.isEmpty()
? Validation.<E, Result<Stream<I>, I>>fail(e.f())
: Validation.<E, Result<Stream<I>, I>>success(result(is.tail()._1(), is.head())));
}
/**
* Returns a parser that negates this parser. If this parser succeeds, then the returned parser
* fails and vice versa.
*
* @param e The error message to fail with if this parser succeeds.
* @return A parser that negates this parser.
*/
public Parser<I, Unit, E> not(final F0<E> e) {
return parser(
i ->
parse(i).isFail()
? Validation.<E, Result<I, Unit>>success(result(i, unit()))
: Validation.<E, Result<I, Unit>>fail(e.f()));
}