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Stream.java
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1809 lines (1653 loc) · 60.2 KB
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package fj.data;
import fj.Effect;
import fj.Equal;
import fj.F;
import fj.F2;
import fj.F3;
import fj.Function;
import fj.Monoid;
import fj.Ord;
import fj.P;
import fj.P1;
import fj.P1Functions;
import fj.P2;
import fj.Unit;
import fj.control.parallel.Promise;
import fj.control.parallel.Strategy;
import fj.Ordering;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import static fj.Bottom.error;
import static fj.Function.compose;
import static fj.Function.constant;
import static fj.Function.curry;
import static fj.Function.flip;
import static fj.Function.identity;
import static fj.P.p;
import static fj.P.p2;
import static fj.Unit.unit;
import static fj.control.parallel.Promise.promise;
import static fj.data.Array.mkArray;
import static fj.data.Option.none;
import static fj.data.Option.some;
import static fj.function.Booleans.not;
import static fj.Ordering.EQ;
import static fj.Ordering.GT;
import static fj.Ordering.LT;
/**
* A lazy (not yet evaluated), immutable, singly linked list.
*
* @version %build.number%
*/
public abstract class Stream<A> implements Iterable<A> {
private Stream() {
}
/**
* Returns an iterator for this stream. This method exists to permit the use in a <code>for</code>-each loop.
*
* @return A iterator for this stream.
*/
public final Iterator<A> iterator() {
return toCollection().iterator();
}
/**
* The first element of the stream or fails for the empty stream.
*
* @return The first element of the stream or fails for the empty stream.
*/
public abstract A head();
/**
* The stream without the first element or fails for the empty stream.
*
* @return The stream without the first element or fails for the empty stream.
*/
public abstract P1<Stream<A>> tail();
/**
* Returns <code>true</code> if this stream is empty, <code>false</code> otherwise.
*
* @return <code>true</code> if this stream is empty, <code>false</code> otherwise.
*/
public final boolean isEmpty() {
return this instanceof Nil;
}
/**
* Returns <code>false</code> if this stream is empty, <code>true</code> otherwise.
*
* @return <code>false</code> if this stream is empty, <code>true</code> otherwise.
*/
public final boolean isNotEmpty() {
return this instanceof Cons;
}
/**
* Performs a reduction on this stream using the given arguments.
*
* @param nil The value to return if this stream is empty.
* @param cons The function to apply to the head and tail of this stream if it is not empty.
* @return A reduction on this stream.
*/
public final <B> B stream(final B nil, final F<A, F<P1<Stream<A>>, B>> cons) {
return isEmpty() ? nil : cons.f(head()).f(tail());
}
/**
* Performs a right-fold reduction across this stream. This function uses O(length) stack space.
*
* @param f The function to apply on each element of the stream.
* @param b The beginning value to start the application from.
* @return The final result after the right-fold reduction.
*/
public final <B> B foldRight(final F<A, F<P1<B>, B>> f, final B b) {
return isEmpty() ? b : f.f(head()).f(new P1<B>() {
public B _1() {
return tail()._1().foldRight(f, b);
}
});
}
/**
* Performs a right-fold reduction across this stream. This function uses O(length) stack space.
*
* @param f The function to apply on each element of the stream.
* @param b The beginning value to start the application from.
* @return The final result after the right-fold reduction.
*/
public final <B> B foldRight(final F2<A, P1<B>, B> f, final B b) {
return foldRight(curry(f), b);
}
/**
* Performs a right-fold reduction across this stream. This function uses O(length) stack space.
*
* @param f The function to apply on each element of the stream.
* @param b The beginning value to start the application from.
* @return The final result after the right-fold reduction.
*/
public final <B> B foldRight1(final F<A, F<B, B>> f, final B b) {
return foldRight(compose(Function.<P1<B>, B, B>andThen().f(P1Functions.<B>__1()), f), b);
}
/**
* Performs a right-fold reduction across this stream. This function uses O(length) stack space.
*
* @param f The function to apply on each element of the stream.
* @param b The beginning value to start the application from.
* @return The final result after the right-fold reduction.
*/
public final <B> B foldRight1(final F2<A, B, B> f, final B b) {
return foldRight1(curry(f), b);
}
/**
* Performs a left-fold reduction across this stream. This function runs in constant space.
*
* @param f The function to apply on each element of the stream.
* @param b The beginning value to start the application from.
* @return The final result after the left-fold reduction.
*/
public final <B> B foldLeft(final F<B, F<A, B>> f, final B b) {
B x = b;
for (Stream<A> xs = this; !xs.isEmpty(); xs = xs.tail()._1())
x = f.f(x).f(xs.head());
return x;
}
/**
* Performs a left-fold reduction across this stream. This function runs in constant space.
*
* @param f The function to apply on each element of the stream.
* @param b The beginning value to start the application from.
* @return The final result after the left-fold reduction.
*/
public final <B> B foldLeft(final F2<B, A, B> f, final B b) {
return foldLeft(curry(f), b);
}
/**
* Takes the first 2 elements of the stream and applies the function to them,
* then applies the function to the result and the third element and so on.
*
* @param f The function to apply on each element of the stream.
* @return The final result after the left-fold reduction.
*/
public final A foldLeft1(final F2<A, A, A> f) {
return foldLeft1(curry(f));
}
/**
* Takes the first 2 elements of the stream and applies the function to them,
* then applies the function to the result and the third element and so on.
*
* @param f The function to apply on each element of the stream.
* @return The final result after the left-fold reduction.
*/
public final A foldLeft1(final F<A, F<A, A>> f) {
if (isEmpty())
throw error("Undefined: foldLeft1 on empty list");
return tail()._1().foldLeft(f, head());
}
/**
* Returns the head of this stream if there is one or the given argument if this stream is empty.
*
* @param a The argument to return if this stream is empty.
* @return The head of this stream if there is one or the given argument if this stream is empty.
*/
public final A orHead(final P1<A> a) {
return isEmpty() ? a._1() : head();
}
/**
* Returns the tail of this stream if there is one or the given argument if this stream is empty.
*
* @param as The argument to return if this stream is empty.
* @return The tail of this stream if there is one or the given argument if this stream is empty.
*/
public final P1<Stream<A>> orTail(final P1<Stream<A>> as) {
return isEmpty() ? as : tail();
}
/**
* Intersperses the given value between each two elements of the stream.
*
* @param a The value to intersperse between values of the stream.
* @return A new stream with the given value between each two elements of the stream.
*/
public final Stream<A> intersperse(final A a) {
return isEmpty() ? this : cons(head(), new P1<Stream<A>>() {
public Stream<A> _1() {
return prefix(a, tail()._1());
}
public Stream<A> prefix(final A x, final Stream<A> xs) {
return xs.isEmpty() ? xs : cons(x, p(cons(xs.head(), new P1<Stream<A>>() {
public Stream<A> _1() {
return prefix(a, xs.tail()._1());
}
})));
}
});
}
/**
* Maps the given function across this stream.
*
* @param f The function to map across this stream.
* @return A new stream after the given function has been applied to each element.
*/
public final <B> Stream<B> map(final F<A, B> f) {
return isEmpty() ? Stream.<B>nil() : cons(f.f(head()), new P1<Stream<B>>() {
public Stream<B> _1() {
return tail()._1().map(f);
}
});
}
/**
* Provides a first-class version of the map function.
*
* @return A function that maps a given function across a given stream.
*/
public static <A, B> F<F<A, B>, F<Stream<A>, Stream<B>>> map_() {
return new F<F<A, B>, F<Stream<A>, Stream<B>>>() {
public F<Stream<A>, Stream<B>> f(final F<A, B> f) {
return new F<Stream<A>, Stream<B>>() {
public Stream<B> f(final Stream<A> as) {
return as.map(f);
}
};
}
};
}
/**
* Performs a side-effect for each element of this stream.
*
* @param f The side-effect to perform for the given element.
* @return The unit value.
*/
public final Unit foreach(final F<A, Unit> f) {
for (Stream<A> xs = this; xs.isNotEmpty(); xs = xs.tail()._1())
f.f(xs.head());
return unit();
}
/**
* Performs a side-effect for each element of this stream.
*
* @param f The side-effect to perform for the given element.
*/
public final void foreach(final Effect<A> f) {
for (Stream<A> xs = this; xs.isNotEmpty(); xs = xs.tail()._1())
f.e(xs.head());
}
/**
* Filters elements from this stream by returning only elements which produce <code>true</code>
* when the given function is applied to them.
*
* @param f The predicate function to filter on.
* @return A new stream whose elements all match the given predicate.
*/
public final Stream<A> filter(final F<A, Boolean> f) {
final Stream<A> as = dropWhile(not(f));
return as.isNotEmpty() ? cons(as.head(), new P1<Stream<A>>() {
public Stream<A> _1() {
return as.tail()._1().filter(f);
}
}) : as;
}
/**
* Appends the given stream to this stream.
*
* @param as The stream to append to this one.
* @return A new stream that has appended the given stream.
*/
public final Stream<A> append(final Stream<A> as) {
return isEmpty() ? as : cons(head(), new P1<Stream<A>>() {
public Stream<A> _1() {
return tail()._1().append(as);
}
});
}
/**
* Appends the given stream to this stream.
*
* @param as The stream to append to this one.
* @return A new stream that has appended the given stream.
*/
public final Stream<A> append(final P1<Stream<A>> as) {
return isEmpty() ? as._1() : cons(head(), new P1<Stream<A>>() {
public Stream<A> _1() {
return tail()._1().append(as);
}
});
}
/**
* Returns a new stream of all the items in this stream that do not appear in the given stream.
*
* @param eq an equality for the items of the streams.
* @param xs a list to subtract from this stream.
* @return a stream of all the items in this stream that do not appear in the given stream.
*/
public final Stream<A> minus(final Equal<A> eq, final Stream<A> xs) {
return removeAll(compose(Monoid.disjunctionMonoid.sumLeftS(), xs.mapM(curry(eq.eq()))));
}
/**
* Filters elements from this stream by returning only elements which produce <code>false</code> when
* the given function is applied to them.
*
* @param f The predicate function to filter on.
* @return A new stream whose elements do not match the given predicate.
*/
public final Stream<A> removeAll(final F<A, Boolean> f) {
return filter(compose(not, f));
}
/**
* Turn a stream of functions into a function returning a stream.
*
* @param fs The stream of functions to sequence into a single function that returns a stream.
* @return A function that, when given an argument, applies all the functions in the given stream to it
* and returns a stream of the results.
*/
public static <A, B> F<B, Stream<A>> sequence_(final Stream<F<B, A>> fs) {
return fs.foldRight(new F2<F<B, A>, P1<F<B, Stream<A>>>, F<B, Stream<A>>>() {
public F<B, Stream<A>> f(final F<B, A> baf, final P1<F<B, Stream<A>>> p1) {
return Function.bind(baf, p1._1(), Function.curry(new F2<A, Stream<A>, Stream<A>>() {
public Stream<A> f(final A a, final Stream<A> stream) {
return cons(a, p(stream));
}
}));
}
}, Function
.<B, Stream<A>>constant(Stream.<A>nil()));
}
/**
* Maps the given function of arity-2 across this stream and returns a function that applies all the resulting
* functions to a given argument.
*
* @param f A function of arity-2
* @return A function that, when given an argument, applies the given function to that argument and every element
* in this list.
*/
public final <B, C> F<B, Stream<C>> mapM(final F<A, F<B, C>> f) {
return sequence_(map(f));
}
/**
* Binds the given function across each element of this stream with a final join.
*
* @param f The function to apply to each element of this stream.
* @return A new stream after performing the map, then final join.
*/
public final <B> Stream<B> bind(final F<A, Stream<B>> f) {
return map(f).foldLeft(new F2<Stream<B>, Stream<B>, Stream<B>>() {
@Override
public Stream<B> f(Stream<B> accumulator, Stream<B> element) {
Stream<B> result = accumulator;
for (B single : element) {
result = result.cons(single);
}
return result;
}
}, Stream.<B>nil()).reverse();
}
/**
* Binds the given function across each element of this stream and the given stream with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given stream.
* @return A new stream after performing the map, then final join.
*/
public final <B, C> Stream<C> bind(final Stream<B> sb, final F<A, F<B, C>> f) {
return sb.apply(map(f));
}
/**
* Binds the given function across each element of this stream and the given stream with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given stream.
* @return A new stream after performing the map, then final join.
*/
public final <B, C> Stream<C> bind(final Stream<B> sb, final F2<A, B, C> f) {
return bind(sb, curry(f));
}
/**
* Binds the given function across each element of this stream and the given streams with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param sc A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given streams.
* @return A new stream after performing the map, then final join.
*/
public final <B, C, D> Stream<D> bind(final Stream<B> sb, final Stream<C> sc, final F<A, F<B, F<C, D>>> f) {
return sc.apply(bind(sb, f));
}
/**
* Binds the given function across each element of this stream and the given streams with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param sc A given stream to bind the given function with.
* @param sd A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given streams.
* @return A new stream after performing the map, then final join.
*/
public final <B, C, D, E> Stream<E> bind(final Stream<B> sb, final Stream<C> sc, final Stream<D> sd,
final F<A, F<B, F<C, F<D, E>>>> f) {
return sd.apply(bind(sb, sc, f));
}
/**
* Binds the given function across each element of this stream and the given streams with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param sc A given stream to bind the given function with.
* @param sd A given stream to bind the given function with.
* @param se A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given streams.
* @return A new stream after performing the map, then final join.
*/
public final <B, C, D, E, F$> Stream<F$> bind(final Stream<B> sb, final Stream<C> sc, final Stream<D> sd,
final Stream<E> se, final F<A, F<B, F<C, F<D, F<E, F$>>>>> f) {
return se.apply(bind(sb, sc, sd, f));
}
/**
* Binds the given function across each element of this stream and the given streams with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param sc A given stream to bind the given function with.
* @param sd A given stream to bind the given function with.
* @param se A given stream to bind the given function with.
* @param sf A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given streams.
* @return A new stream after performing the map, then final join.
*/
public final <B, C, D, E, F$, G> Stream<G> bind(final Stream<B> sb, final Stream<C> sc, final Stream<D> sd,
final Stream<E> se, final Stream<F$> sf,
final F<A, F<B, F<C, F<D, F<E, F<F$, G>>>>>> f) {
return sf.apply(bind(sb, sc, sd, se, f));
}
/**
* Binds the given function across each element of this stream and the given streams with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param sc A given stream to bind the given function with.
* @param sd A given stream to bind the given function with.
* @param se A given stream to bind the given function with.
* @param sf A given stream to bind the given function with.
* @param sg A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given streams.
* @return A new stream after performing the map, then final join.
*/
public final <B, C, D, E, F$, G, H> Stream<H> bind(final Stream<B> sb, final Stream<C> sc, final Stream<D> sd,
final Stream<E> se, final Stream<F$> sf, final Stream<G> sg,
final F<A, F<B, F<C, F<D, F<E, F<F$, F<G, H>>>>>>> f) {
return sg.apply(bind(sb, sc, sd, se, sf, f));
}
/**
* Binds the given function across each element of this stream and the given streams with a final
* join.
*
* @param sb A given stream to bind the given function with.
* @param sc A given stream to bind the given function with.
* @param sd A given stream to bind the given function with.
* @param se A given stream to bind the given function with.
* @param sf A given stream to bind the given function with.
* @param sg A given stream to bind the given function with.
* @param sh A given stream to bind the given function with.
* @param f The function to apply to each element of this stream and the given streams.
* @return A new stream after performing the map, then final join.
*/
public final <B, C, D, E, F$, G, H, I> Stream<I> bind(final Stream<B> sb, final Stream<C> sc, final Stream<D> sd,
final Stream<E> se, final Stream<F$> sf, final Stream<G> sg,
final Stream<H> sh,
final F<A, F<B, F<C, F<D, F<E, F<F$, F<G, F<H, I>>>>>>>> f) {
return sh.apply(bind(sb, sc, sd, se, sf, sg, f));
}
/**
* Performs a bind across each stream element, but ignores the element value each time.
*
* @param bs The stream to apply in the final join.
* @return A new stream after the final join.
*/
public final <B> Stream<B> sequence(final Stream<B> bs) {
final F<A, Stream<B>> c = constant(bs);
return bind(c);
}
/**
* Performs function application within a stream (applicative functor pattern).
*
* @param sf The stream of functions to apply.
* @return A new stream after applying the given stream of functions through this stream.
*/
public final <B> Stream<B> apply(final Stream<F<A, B>> sf) {
return sf.bind(new F<F<A, B>, Stream<B>>() {
public Stream<B> f(final F<A, B> f) {
return map(new F<A, B>() {
public B f(final A a) {
return f.f(a);
}
});
}
});
}
/**
* Interleaves the given stream with this stream to produce a new stream.
*
* @param as The stream to interleave this stream with.
* @return A new stream with elements interleaved from this stream and the given stream.
*/
public final Stream<A> interleave(final Stream<A> as) {
return isEmpty() ? as : as.isEmpty() ? this : cons(head(), new P1<Stream<A>>() {
@Override public Stream<A> _1() {
return as.interleave(tail()._1());
}
});
}
/**
* Sort this stream according to the given ordering.
*
* @param o An ordering for the elements of this stream.
* @return A new stream with the elements of this stream sorted according to the given ordering.
*/
public final Stream<A> sort(final Ord<A> o) {
return mergesort(o, map(flip(Stream.<A>cons()).f(p(Stream.<A>nil()))));
}
// Merges a stream of individually sorted streams into a single sorted stream.
private static <A> Stream<A> mergesort(final Ord<A> o, final Stream<Stream<A>> s) {
if (s.isEmpty())
return nil();
Stream<Stream<A>> xss = s;
while (xss.tail()._1().isNotEmpty())
xss = mergePairs(o, xss);
return xss.head();
}
// Merges individually sorted streams two at a time.
private static <A> Stream<Stream<A>> mergePairs(final Ord<A> o, final Stream<Stream<A>> s) {
if (s.isEmpty() || s.tail()._1().isEmpty())
return s;
final Stream<Stream<A>> t = s.tail()._1();
return cons(merge(o, s.head(), t.head()), new P1<Stream<Stream<A>>>() {
public Stream<Stream<A>> _1() {
return mergePairs(o, t.tail()._1());
}
});
}
// Merges two individually sorted streams.
private static <A> Stream<A> merge(final Ord<A> o, final Stream<A> xs, final Stream<A> ys) {
if (xs.isEmpty())
return ys;
if (ys.isEmpty())
return xs;
final A x = xs.head();
final A y = ys.head();
if (o.isGreaterThan(x, y))
return cons(y, new P1<Stream<A>>() {
public Stream<A> _1() {
return merge(o, xs, ys.tail()._1());
}
});
return cons(x, new P1<Stream<A>>() {
public Stream<A> _1() {
return merge(o, xs.tail()._1(), ys);
}
});
}
/**
* Sort this stream according to the given ordering, using a parallel Quick Sort algorithm that uses the given
* parallelisation strategy.
*
* @param o An ordering for the elements of this stream.
* @param s A strategy for parallelising the algorithm.
* @return A new stream with the elements of this stream sorted according to the given ordering.
*/
public final Stream<A> sort(final Ord<A> o, final Strategy<Unit> s) {
return qs(o, s).claim();
}
private Promise<Stream<A>> qs(final Ord<A> o, final Strategy<Unit> s) {
if (isEmpty())
return promise(s, P.p(this));
else {
final F<Boolean, Boolean> id = identity();
final A x = head();
final P1<Stream<A>> xs = tail();
final Promise<Stream<A>> left = Promise.join(s, P1Functions.map(xs, flt(o, s, x, id)));
final Promise<Stream<A>> right = P1Functions.map(xs, flt(o, s, x, not))._1();
final Monoid<Stream<A>> m = Monoid.streamMonoid();
return right.fmap(m.sum(single(x))).apply(left.fmap(m.sum()));
}
}
private static <A> F<Stream<A>, Promise<Stream<A>>> qs_(final Ord<A> o, final Strategy<Unit> s) {
return new F<Stream<A>, Promise<Stream<A>>>() {
public Promise<Stream<A>> f(final Stream<A> xs) {
return xs.qs(o, s);
}
};
}
private static <A> F<Stream<A>, Promise<Stream<A>>> flt(final Ord<A> o,
final Strategy<Unit> s,
final A x,
final F<Boolean, Boolean> f) {
final F<F<A, Boolean>, F<Stream<A>, Stream<A>>> filter = filter();
final F<A, Boolean> lt = o.isLessThan(x);
return compose(qs_(o, s), filter.f(compose(f, lt)));
}
/**
* Projects an immutable collection of this stream.
*
* @return An immutable collection of this stream.
*/
public final Collection<A> toCollection() {
return new AbstractCollection<A>() {
public Iterator<A> iterator() {
return new Iterator<A>() {
private Stream<A> xs = Stream.this;
public boolean hasNext() {
return xs.isNotEmpty();
}
public A next() {
if (xs.isEmpty())
throw new NoSuchElementException();
else {
final A a = xs.head();
xs = xs.tail()._1();
return a;
}
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public int size() {
return length();
}
};
}
/**
* Returns a stream of integers from the given <code>from</code> value (inclusive) to the given
* <code>to</code> value (exclusive).
*
* @param from The minimum value for the stream (inclusive).
* @param to The maximum value for the stream (exclusive).
* @return A stream of integers from the given <code>from</code> value (inclusive) to the given
* <code>to</code> value (exclusive).
*/
public static Stream<Integer> range(final int from, final long to) {
return from >= to ? Stream.<Integer>nil() : cons(from, new P1<Stream<Integer>>() {
public Stream<Integer> _1() {
return range(from + 1, to);
}
});
}
/**
* Constructs a stream with the given elements.
*
* @param as The elements which which to construct a stream.
* @return a new stream with the given elements.
*/
public static <A> Stream<A> stream(final A... as) {
return as.length == 0 ? Stream.<A>nil()
: unfold(P2.tuple(new F2<A[], Integer, Option<P2<A, P2<A[], Integer>>>>() {
public Option<P2<A, P2<A[], Integer>>> f(final A[] as, final Integer i) {
return i >= as.length ? Option.<P2<A, P2<A[], Integer>>>none()
: some(P.p(as[i], P.p(as, i + 1)));
}
}), P.p(as, 0));
}
/**
* Returns a stream that is either infinite or bounded up to the maximum value of the given iterator starting at the
* given value and stepping at increments of <code>1</code>.
*
* @param e The enumerator to compute successors from.
* @param from The value to begin computing successors from.
* @return A stream that is either infinite or bounded up to the maximum value of the given iterator starting at the
* given value and stepping at increments of <code>1</code>.
*/
public static <A> Stream<A> forever(final Enumerator<A> e, final A from) {
return forever(e, from, 1L);
}
/**
* Returns a stream that is either infinite or bounded up to the maximum value of the given iterator starting at the
* given value and stepping at the given increment.
*
* @param e The enumerator to compute successors from.
* @param from The value to begin computing successors from.
* @param step The increment to step.
* @return A stream that is either infinite or bounded up to the maximum value of the given iterator starting at the
* given value and stepping at the given increment.
*/
public static <A> Stream<A> forever(final Enumerator<A> e, final A from, final long step) {
return cons(from, new P1<Stream<A>>() {
public Stream<A> _1() {
return e.plus(from, step).map(new F<A, Stream<A>>() {
public Stream<A> f(final A a) {
return forever(e, a, step);
}
}).orSome(Stream.<A>nil());
}
});
}
/**
* Returns a stream using the given enumerator from the given value to the other given value stepping at increments of
* <code>1</code>.
*
* @param e The enumerator to compute successors from.
* @param from The value to begin computing successors from.
* @param to The value to stop computing successors from.
* @return A stream using the given enumerator from the given value to the other given value stepping at increments of
* <code>1</code>.
*/
public static <A> Stream<A> range(final Enumerator<A> e, final A from, final A to) {
return range(e, from, to, 1L);
}
/**
* Returns a stream using the given enumerator from the given value to the other given value stepping at the given
* increment.
*
* @param e The enumerator to compute successors from.
* @param from The value to begin computing successors from.
* @param to The value to stop computing successors from.
* @param step The increment to step.
* @return A stream using the given enumerator from the given value to the other given value stepping at the given
* increment.
*/
public static <A> Stream<A> range(final Enumerator<A> e, final A from, final A to, final long step) {
final Ordering o = e.order().compare(from, to);
return o == EQ || step > 0L && o == GT || step < 0L && o == LT ? single(from) : cons(from, new P1<Stream<A>>() {
public Stream<A> _1() {
return Stream.join(e.plus(from, step).filter(new F<A, Boolean>() {
public Boolean f(final A a) {
return !(o == LT ? e.order().isLessThan(to, a) : e.order().isGreaterThan(to, a));
}
}).map(new F<A, Stream<A>>() {
public Stream<A> f(final A a) {
return range(e, a, to, step);
}
}).toStream());
}
});
}
/**
* Returns an infinite stream of integers from the given <code>from</code> value (inclusive).
*
* @param from The minimum value for the stream (inclusive).
* @return A stream of integers from the given <code>from</code> value (inclusive).
*/
public static Stream<Integer> range(final int from) {
return cons(from, new P1<Stream<Integer>>() {
public Stream<Integer> _1() {
return range(from + 1);
}
});
}
/**
* Returns a first-class version of the filter function.
*
* @return a function that filters a given stream using a given predicate.
*/
public static <A> F<F<A, Boolean>, F<Stream<A>, Stream<A>>> filter() {
return curry(new F2<F<A, Boolean>, Stream<A>, Stream<A>>() {
public Stream<A> f(final F<A, Boolean> f, final Stream<A> as) {
return as.filter(f);
}
});
}
/**
* Zips this stream with the given stream of functions, applying each function in turn to the
* corresponding element in this stream to produce a new stream. If this stream and the given stream
* have different lengths, then the longer stream is normalised so this function never fails.
*
* @param fs The stream of functions to apply to this stream.
* @return A new stream with a length the same as the shortest of this stream and the given stream.
*/
public final <B> Stream<B> zapp(final Stream<F<A, B>> fs) {
return fs.isEmpty() || isEmpty() ? Stream.<B>nil() :
cons(fs.head().f(head()), new P1<Stream<B>>() {
public Stream<B> _1() {
return tail()._1().zapp(fs.tail()._1());
}
});
}
/**
* Zips this stream with the given stream using the given function to produce a new stream. If
* this stream and the given stream have different lengths, then the longer stream is normalised
* so this function never fails.
*
* @param bs The stream to zip this stream with.
* @param f The function to zip this stream and the given stream with.
* @return A new stream with a length the same as the shortest of this stream and the given
* stream.
*/
public final <B, C> Stream<C> zipWith(final Stream<B> bs, final F<A, F<B, C>> f) {
return bs.zapp(zapp(repeat(f)));
}
/**
* Zips this stream with the given stream using the given function to produce a new stream. If
* this stream and the given stream have different lengths, then the longer stream is normalised
* so this function never fails.
*
* @param bs The stream to zip this stream with.
* @param f The function to zip this stream and the given stream with.
* @return A new stream with a length the same as the shortest of this stream and the given
* stream.
*/
public final <B, C> Stream<C> zipWith(final Stream<B> bs, final F2<A, B, C> f) {
return zipWith(bs, curry(f));
}
/**
* Partially-applied version of zipWith.
* Returns a function that zips a given stream with this stream using the given function.
*
* @param f The function to zip this stream and a given stream with.
* @return A function that zips a given stream with this stream using the given function.
*/
public final <B, C> F<Stream<B>, Stream<C>> zipWith(final F<A, F<B, C>> f) {
return new F<Stream<B>, Stream<C>>() {
public Stream<C> f(final Stream<B> stream) {
return zipWith(stream, f);
}
};
}
/**
* Zips this stream with the given stream to produce a stream of pairs. If this stream and the
* given stream have different lengths, then the longer stream is normalised so this function
* never fails.
*
* @param bs The stream to zip this stream with.
* @return A new stream with a length the same as the shortest of this stream and the given
* stream.
*/
public final <B> Stream<P2<A, B>> zip(final Stream<B> bs) {
final F<A, F<B, P2<A, B>>> __2 = p2();
return zipWith(bs, __2);
}
/**
* Zips this stream with the index of its element as a pair.
*
* @return A new stream with the same length as this stream.
*/
public final Stream<P2<A, Integer>> zipIndex() {
return zipWith(range(0), new F2<A, Integer, P2<A, Integer>>() {
public P2<A, Integer> f(final A a, final Integer i) {
return p(a, i);
}
});
}
/**
* Returns an either projection of this stream; the given argument in <code>Left</code> if empty,
* or the first element in <code>Right</code>.
*
* @param x The value to return in left if this stream is empty.
* @return An either projection of this stream.
*/
public final <X> Either<X, A> toEither(final P1<X> x) {
return isEmpty() ? Either.<X, A>left(x._1()) : Either.<X, A>right(head());
}
/**
* Returns an option projection of this stream; <code>None</code> if empty, or the first element
* in <code>Some</code>.
*
* @return An option projection of this stream.
*/
public final Option<A> toOption() {
return isEmpty() ? Option.<A>none() : some(head());
}
/**
* Returns a list projection of this stream.
*
* @return A list projection of this stream.
*/
public final List<A> toList() {
List<A> as = List.nil();
for (Stream<A> x = this; !x.isEmpty(); x = x.tail()._1()) {
as = as.snoc(x.head());
}
return as;
}
/**
* Returns a array projection of this stream.
*
* @return A array projection of this stream.
*/
@SuppressWarnings({"unchecked"})
public final Array<A> toArray() {
final int l = length();
final Object[] a = new Object[l];
Stream<A> x = this;
for (int i = 0; i < l; i++) {
a[i] = x.head();
x = x.tail()._1();
}
return mkArray(a);
}
/**
* Returns a array projection of this stream.
*