src/main/java/software/kes/enhancediterables/NonEmptyIterable.java
package software.kes.enhancediterables;
import com.jnape.palatable.lambda.adt.Maybe;
import com.jnape.palatable.lambda.functions.Fn1;
import com.jnape.palatable.lambda.functions.Fn2;
import com.jnape.palatable.lambda.functions.builtin.fn2.Cons;
import com.jnape.palatable.lambda.functions.builtin.fn2.Intersperse;
import com.jnape.palatable.lambda.functions.builtin.fn2.MagnetizeBy;
import com.jnape.palatable.lambda.functions.builtin.fn2.Map;
import com.jnape.palatable.lambda.functions.builtin.fn2.PrependAll;
import com.jnape.palatable.lambda.functions.builtin.fn3.ZipWith;
import com.jnape.palatable.lambda.monoid.builtin.Concat;
import java.util.Iterator;
import static com.jnape.palatable.lambda.adt.Maybe.just;
import static java.util.Objects.requireNonNull;
import static software.kes.enhancediterables.EnhancedIterables.unsafeNonEmptyFiniteIterable;
import static software.kes.enhancediterables.EnhancedIterables.unsafeNonEmptyIterable;
import static software.kes.enhancediterables.Wrapped.unwrap;
/**
* An {@code EnhancedIterable} that is guaranteed to contain at least one element.
* <p>
* May be infinite or finite.
*
* @param <A> the element type
*/
public interface NonEmptyIterable<A> extends EnhancedIterable<A> {
/**
* Returns the first element.
*
* @return an element of type {@code A}
*/
A head();
/**
* Returns an {@code EnhancedIterable} containing all subsequent elements of this one beyond the first.
*
* @return an {@code EnhancedIterable<A>}
*/
EnhancedIterable<A> tail();
/**
* Lazily concatenates an {@code Iterable} to the end of this {@code NonEmptyIterable},
* yielding a new {@code NonEmptyIterable}.
*
* @param other an {@link Iterable}
* @return a {@code NonEmptyIterable<A>}
*/
@Override
default NonEmptyIterable<A> concat(Iterable<A> other) {
requireNonNull(other);
return unsafeNonEmptyIterable(Concat.concat(unwrap(this), unwrap(other)));
}
/**
* Returns a new {@code NonEmptyIterable} by applying a function to all elements of this {@code NonEmptyIterable}.
*
* @param f a function from {@code A} to {@code B}.
* This function should be referentially transparent and not perform side-effects.
* It may be called zero or more times for each element.
* @param <B> the type returned by {@code f}
* @return a {@code NonEmptyIterable<B>}
*/
@Override
default <B> NonEmptyIterable<B> fmap(Fn1<? super A, ? extends B> f) {
requireNonNull(f);
return unsafeNonEmptyIterable(Map.map(f, unwrap(this)));
}
/**
* Always returns false, as a {@code NonEmptyIterable} is never empty.
*
* @return false
*/
@Override
default boolean isEmpty() {
return false;
}
/**
* Returns a new {@code NonEmptyIterable} with the provided separator value injected between each value of this
* {@code NonEmptyIterable}.
* <p>
* If this {@code NonEmptyIterable} contains only one element, it is left untouched.
*
* @param separator the separator value
* @return a {@code NonEmptyIterable<A>}
*/
@Override
default NonEmptyIterable<A> intersperse(A separator) {
return unsafeNonEmptyIterable(Intersperse.intersperse(separator, unwrap(this)));
}
/**
* {@inheritDoc}
*/
@Override
default Iterator<A> iterator() {
return Cons.cons(head(), tail()).iterator();
}
/**
* Returns an {@code Iterable} of contiguous groups of elements in this {@code NonEmptyIterable} that match a
* predicate pairwise.
*
* @param predicate the predicate function.
* This function should be referentially transparent and not perform side-effects.
* It may be called zero or more times for each element.
* @return an {@code NonEmptyIterable<NonEmptyIterable<A>>} containing the contiguous groups
*/
@Override
default NonEmptyIterable<? extends NonEmptyIterable<A>> magnetizeBy(Fn2<A, A, Boolean> predicate) {
requireNonNull(predicate);
return unsafeNonEmptyIterable(MagnetizeBy.magnetizeBy(predicate, unwrap(this)))
.fmap(EnhancedIterables::unsafeNonEmptyIterable);
}
/**
* Returns a new {@code NonEmptyIterable} with the provided separator value injected before each value of this
* {@code NonEmptyIterable}.
*
* @param separator the separator value
* @return a {@code NonEmptyIterable<A>}
*/
@Override
default NonEmptyIterable<A> prependAll(A separator) {
return unsafeNonEmptyIterable(PrependAll.prependAll(separator, unwrap(this)));
}
/**
* Converts this {@code NonEmptyIterable} to an {@code NonEmptyFiniteIterable} if there is enough
* information to do so without iterating it.
* <p>
* Note that if this method returns {@code nothing()}, it does NOT necessarily mean this
* {@code NonEmptyIterable} is infinite.
*
* @return a {@code Maybe<NonEmptyFiniteIterable<A>}
*/
@Override
default Maybe<? extends NonEmptyFiniteIterable<A>> toFinite() {
return EnhancedIterables.nonEmptyMaybeFinite(head(), tail());
}
/**
* Always succeeds because {@code NonEmptyIterable}s are always non-empty.
*
* @return this {@code NonEmptyIterable} wrapped in a `just`
*/
@Override
default Maybe<? extends NonEmptyIterable<A>> toNonEmpty() {
return just(this);
}
/**
* Zips together this {@code NonEmptyIterable} with another {@code NonEmptyIterable} by applying a zipping function.
* <p>
* Applies the function to the successive elements of each {@code Iterable} until one of them runs out of elements.
*
* @param fn the zipping function.
* Not null.
* This function should be referentially transparent and not perform side-effects.
* It may be called zero or more times for each element.
* @param other the other {@code Iterable}
* @param <B> the element type of the other {@code Iterable}
* @param <C> the element type of the result
* @return an {@code NonEmptyIterable<C>}
*/
default <B, C> NonEmptyIterable<C> zipWith(Fn2<A, B, C> fn, NonEmptyIterable<B> other) {
requireNonNull(fn);
requireNonNull(other);
return nonEmptyIterable(fn.apply(head(), other.head()),
ZipWith.zipWith(fn, tail(), other.tail()));
}
/**
* Zips together this {@code NonEmptyIterable} with a {@code NonEmptyFiniteIterable} by applying a zipping function.
* <p>
* Applies the function to the successive elements of each {@code Iterable} until one of them runs out of elements.
*
* @param fn the zipping function.
* Not null.
* This function should be referentially transparent and not perform side-effects.
* It may be called zero or more times for each element.
* @param other the other {@code Iterable}
* @param <B> the element type of the other {@code Iterable}
* @param <C> the element type of the result
* @return an {@code NonEmptyFiniteIterable<C>}
*/
default <B, C> NonEmptyFiniteIterable<C> zipWith(Fn2<A, B, C> fn, NonEmptyFiniteIterable<B> other) {
requireNonNull(fn);
requireNonNull(other);
return unsafeNonEmptyFiniteIterable(ZipWith.zipWith(fn, unwrap(this), unwrap(other)));
}
/**
* Creates a {@link NonEmptyIterable}.
*
* @param head the first element
* @param tail the remaining elements. May be empty.
* @param <A> the element type
* @return a {@code NonEmptyIterable<A>}
*/
static <A> NonEmptyIterable<A> nonEmptyIterable(A head, Iterable<A> tail) {
return EnhancedIterables.nonEmptyIterable(head, tail);
}
/**
* Creates a {@code NonEmptyIterable} containing the given elements.
* <p>
* Note that this method actually returns an {@link ImmutableNonEmptyFiniteIterable}, which is
* also a {@link NonEmptyIterable}.
*
* @param first the first element
* @param more the remaining elements
* @param <A> the element type
* @return an {@code ImmutableNonEmptyFiniteIterable<A>}
*/
@SuppressWarnings("varargs")
@SafeVarargs
static <A> ImmutableNonEmptyFiniteIterable<A> of(A first, A... more) {
if (more.length > 0) {
return EnhancedIterables.of(first, more);
} else {
return EnhancedIterables.singleton(first);
}
}
/**
* Returns an infinite {@code ImmutableNonEmptyIterable} that repeatedly iterates a given element.
*
* @param element the value to repeat
* @param <A> the element type
* @return an {@code ImmutableNonEmptyIterable<A>}
*/
static <A> ImmutableNonEmptyIterable<A> repeat(A element) {
return EnhancedIterables.repeat(element);
}
}