/**
* Sequences through the right side of the either monad with a list of values.
*
* @param a The list of values to sequence with the either monad.
* @return A sequenced value.
*/
public static <B, X> Either<X, List<B>> sequenceRight(final List<Either<X, B>> a) {
return a.isEmpty()
? Either.<X, List<B>>right(List.<B>nil())
: a.head()
.right()
.bind(
new Func<B, Either<X, List<B>>>() {
public Either<X, List<B>> f(final B bb) {
return sequenceRight(a.tail()).right().map(cons_(bb));
}
});
}
/**
* Sequences through the left side of the either monad with a list of values.
*
* @param a The list of values to sequence with the either monad.
* @return A sequenced value.
*/
public static <A, X> Either<List<A>, X> sequenceLeft(final List<Either<A, X>> a) {
return a.isEmpty()
? Either.<List<A>, X>left(List.<A>nil())
: a.head()
.left()
.bind(
new Func<A, Either<List<A>, X>>() {
public Either<List<A>, X> f(final A aa) {
return sequenceLeft(a.tail()).left().map(cons_(aa));
}
});
}
/**
* Takes an <code>Either</code> to its contained value within left or right.
*
* @param e The either to reduce.
* @return An <code>Either</code> to its contained value within left or right.
*/
public static <A> A reduce(final Either<A, A> e) {
return e.isLeft() ? e.left().value() : e.right().value();
}
/**
* Binds the given function across this projection's value if it has one.
*
* @param f The function to bind across this projection.
* @return A new either value after binding.
*/
public <X> Either<A, X> bind(final Func<B, Either<A, X>> f) {
return isRight() ? f.f(value()) : new Left<A, X>(e.left().value());
}
/**
* The value of this projection or the result of the given function on the opposing projection's
* value.
*
* @param f The function to execute if this projection has no value.
* @return The value of this projection or the result of the given function on the opposing
* projection's value.
*/
public B on(final Func<A, B> f) {
return isRight() ? value() : f.f(e.left().value());
}
/**
* Map the given function across this projection's value if it has one.
*
* @param f The function to map across this projection.
* @return A new either value after mapping.
*/
public <X> Either<A, X> map(final Func<B, X> f) {
return isRight() ? new Right<A, X>(f.f(value())) : new Left<A, X>(e.left().value());
}
/**
* Returns the value of this projection or fails with the given error message.
*
* @param err The error message to fail with.
* @return The value of this projection
*/
public B valueE(final P1<String> err) {
if (e.isRight())
//noinspection CastToConcreteClass
return ((Right<A, B>) e).b;
else throw error(err._1());
}
/**
* Binds the given function across this projection's value if it has one.
*
* @param f The function to bind across this projection.
* @return A new either value after binding.
*/
public <X> Either<X, B> bind(final Func<A, Either<X, B>> f) {
return isLeft() ? f.f(value()) : new Right<X, B>(e.right().value());
}
/**
* Map the given function across this projection's value if it has one.
*
* @param f The function to map across this projection.
* @return A new either value after mapping.
*/
public <X> Either<X, B> map(final Func<A, X> f) {
return isLeft() ? new Left<X, B>(f.f(value())) : new Right<X, B>(e.right().value());
}
/**
* The value of this projection or the result of the given function on the opposing projection's
* value.
*
* @param f The function to execute if this projection has no value.
* @return The value of this projection or the result of the given function on the opposing
* projection's value.
*/
public A on(final Func<B, A> f) {
return isLeft() ? value() : f.f(e.right().value());
}
/**
* Returns the value of this projection or fails with the given error message.
*
* @param err The error message to fail with.
* @return The value of this projection
*/
public A valueE(final P1<String> err) {
if (e.isLeft())
//noinspection CastToConcreteClass
return ((Left<A, B>) e).a;
else throw error(err._1());
}