1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
|
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.collection
package immutable
import generic._
import mutable.{Builder, StringBuilder, LazyBuilder, ListBuffer}
import scala.annotation.tailrec
import Stream.cons
/** The class `Stream` implements lazy lists where elements
* are only evaluated when they are needed. Here is an example:
*
* {{{
* object Main extends Application {
*
* def from(n: Int): Stream[Int] =
* Stream.cons(n, from(n + 1))
*
* def sieve(s: Stream[Int]): Stream[Int] =
* Stream.cons(s.head, sieve(s.tail filter { _ % s.head != 0 }))
*
* def primes = sieve(from(2))
*
* primes take 10 print
* }
* }}}
*
* @tparam A the type of the elements contained in this stream.
*
* @author Martin Odersky, Matthias Zenger
* @version 1.1 08/08/03
* @since 2.8
* @define Coll Stream
* @define coll stream
* @define orderDependent
* @define orderDependentFold
*/
abstract class Stream[+A] extends LinearSeq[A]
with GenericTraversableTemplate[A, Stream]
with LinearSeqOptimized[A, Stream[A]] {
self =>
override def companion: GenericCompanion[Stream] = Stream
import scala.collection.{Traversable, Iterable, Seq, IndexedSeq}
/** is this stream empty? */
def isEmpty: Boolean
/** The first element of this stream
* @throws Predef.NoSuchElementException if the stream is empty.
*/
def head: A
/** A stream consisting of the remaining elements of this stream after the first one.
* @throws Predef.UnsupportedOperationException if the stream is empty.
*/
def tail: Stream[A]
/** Is the tail of this stream defined? */
protected def tailDefined: Boolean
// Implementation of abstract method in Traversable
// New methods in Stream
/** The stream resulting from the concatenation of this stream with the argument stream.
* @param rest The stream that gets appended to this stream
* @return The stream containing elements of this stream and the traversable object.
*/
def append[B >: A](rest: => TraversableOnce[B]): Stream[B] =
if (isEmpty) rest.toStream else cons(head, tail append rest)
/** Forces evaluation of the whole stream and returns it. */
def force: Stream[A] = {
var these = this
while (!these.isEmpty) these = these.tail
this
}
/** Prints elements of this stream one by one, separated by commas. */
def print() { print(", ") }
/** Prints elements of this stream one by one, separated by `sep`.
* @param sep The separator string printed between consecutive elements.
*/
def print(sep: String) {
def loop(these: Stream[A], start: String) {
Console.print(start)
if (these.isEmpty) Console.print("empty")
else {
Console.print(these.head)
loop(these.tail, sep)
}
}
loop(this, "")
}
override def length: Int = {
var len = 0
var left = this
while (!left.isEmpty) {
len += 1
left = left.tail
}
len
}
/** It's an imperfect world, but at least we can bottle up the
* imperfection in a capsule.
*/
@inline private def asThat[That](x: AnyRef): That = x.asInstanceOf[That]
@inline private def asStream[B](x: AnyRef): Stream[B] = x.asInstanceOf[Stream[B]]
@inline private def isStreamBuilder[B, That](bf: CanBuildFrom[Stream[A], B, That]) =
bf(repr).isInstanceOf[Stream.StreamBuilder[_]]
// Overridden methods from Traversable
override def toStream: Stream[A] = this
override def hasDefiniteSize = {
def loop(s: Stream[A]): Boolean = s.isEmpty || s.tailDefined && loop(s.tail)
loop(this)
}
/** Create a new stream which contains all elements of this stream
* followed by all elements of Traversable `that`.
* @note It's subtle why this works. We know that if the target type
* of the Builder That is either a Stream, or one of its supertypes, or undefined,
* then StreamBuilder will be chosen for the implicit.
* we recognize that fact and optimize to get more laziness.
*/
override def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That =
// we assume there is no other builder factory on streams and therefore know that That = Stream[A]
if (isStreamBuilder(bf)) asThat(
if (isEmpty) that.toStream
else cons(head, asStream[A](tail ++ that))
)
else super.++(that)(bf)
override def +:[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That =
if (isStreamBuilder(bf)) asThat(cons(elem, this))
else super.+:(elem)(bf)
/**
* Create a new stream which contains all intermediate results of applying the operator
* to subsequent elements left to right.
* @note This works because the target type of the Builder That is a Stream.
*/
override final def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That =
if (isStreamBuilder(bf)) asThat(
if (isEmpty) Stream(z)
else cons(z, asStream[B](tail.scanLeft(op(z, head))(op)))
)
else super.scanLeft(z)(op)(bf)
/** Returns the stream resulting from applying the given function
* `f` to each element of this stream.
*
* @param f function to apply to each element.
* @return <code>f(a<sub>0</sub>), ..., f(a<sub>n</sub>)</code> if this
* sequence is <code>a<sub>0</sub>, ..., a<sub>n</sub></code>.
*/
override final def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That = {
if (isStreamBuilder(bf)) asThat(
if (isEmpty) Stream.Empty
else cons(f(head), asStream[B](tail map f))
)
else super.map(f)(bf)
}
override final def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That = {
if (!isStreamBuilder(bf)) super.collect(pf)(bf)
else {
// this implementation avoids:
// 1) stackoverflows (could be achieved with tailrec, too)
// 2) out of memory errors for big streams (`this` reference can be eliminated from the stack)
var rest: Stream[A] = this
while (rest.nonEmpty && !pf.isDefinedAt(rest.head)) rest = rest.tail
// without the call to the companion object, a thunk is created for the tail of the new stream,
// and the closure of the thunk will reference `this`
if (rest.isEmpty) Stream.Empty.asInstanceOf[That]
else Stream.collectedTail(rest, pf, bf).asInstanceOf[That]
}
}
/** Applies the given function `f` to each element of
* this stream, then concatenates the results.
*
* @param f the function to apply on each element.
* @param bf $bfinfo
* @return <code>f(a<sub>0</sub>) ::: ... ::: f(a<sub>n</sub>)</code> if
* this stream is <code>[a<sub>0</sub>, ..., a<sub>n</sub>]</code>.
*/
override final def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That =
// we assume there is no other builder factory on streams and therefore know that That = Stream[B]
// optimisations are not for speed, but for functionality
// see tickets #153, #498, #2147, and corresponding tests in run/ (as well as run/stream_flatmap_odds.scala)
if (isStreamBuilder(bf)) asThat(
if (isEmpty) Stream.Empty
else {
// establish !prefix.isEmpty || nonEmptyPrefix.isEmpty
var nonEmptyPrefix = this
var prefix = f(nonEmptyPrefix.head).toStream
while (!nonEmptyPrefix.isEmpty && prefix.isEmpty) {
nonEmptyPrefix = nonEmptyPrefix.tail
if(!nonEmptyPrefix.isEmpty)
prefix = f(nonEmptyPrefix.head).toStream
}
if (nonEmptyPrefix.isEmpty) Stream.empty
else prefix append asStream[B](nonEmptyPrefix.tail flatMap f)
}
)
else super.flatMap(f)(bf)
/** Returns all the elements of this stream that satisfy the
* predicate <code>p</code>. The order of the elements is preserved.
*
* @param p the predicate used to filter the stream.
* @return the elements of this stream satisfying <code>p</code>.
*/
override def filter(p: A => Boolean): Stream[A] = {
// optimization: drop leading prefix of elems for which f returns false
// var rest = this dropWhile (!p(_)) - forget DRY principle - GC can't collect otherwise
var rest = this
while (!rest.isEmpty && !p(rest.head)) rest = rest.tail
// private utility func to avoid `this` on stack (would be needed for the lazy arg)
if (rest.nonEmpty) Stream.filteredTail(rest, p)
else Stream.Empty
}
override final def withFilter(p: A => Boolean): StreamWithFilter = new StreamWithFilter(p)
/** A lazier implementation of WithFilter than TraversableLike's.
*/
final class StreamWithFilter(p: A => Boolean) extends WithFilter(p) {
override def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That = {
def tailMap = asStream[B](tail withFilter p map f)
if (isStreamBuilder(bf)) asThat(
if (isEmpty) Stream.Empty
else if (p(head)) cons(f(head), tailMap)
else tailMap
)
else super.map(f)(bf)
}
override def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Stream[A], B, That]): That = {
def tailFlatMap = asStream[B](tail withFilter p flatMap f)
if (isStreamBuilder(bf)) asThat(
if (isEmpty) Stream.Empty
else if (p(head)) f(head).toStream append tailFlatMap
else tailFlatMap
)
else super.flatMap(f)(bf)
}
override def foreach[B](f: A => B) =
for (x <- self)
if (p(x)) f(x)
override def withFilter(q: A => Boolean): StreamWithFilter =
new StreamWithFilter(x => p(x) && q(x))
}
/** A lazier Iterator than LinearSeqLike's. */
override def iterator: Iterator[A] = new StreamIterator(self)
/** Apply the given function <code>f</code> to each element of this linear sequence
* (while respecting the order of the elements).
*
* @param f the treatment to apply to each element.
* @note Overridden here as final to trigger tail-call optimization, which replaces
* 'this' with 'tail' at each iteration. This is absolutely necessary
* for allowing the GC to collect the underlying stream as elements are
* consumed.
*/
@tailrec
override final def foreach[B](f: A => B) {
if (!this.isEmpty) {
f(head)
tail.foreach(f)
}
}
/** Stream specialization of foldLeft which allows GC to collect
* along the way.
*/
@tailrec
override final def foldLeft[B](z: B)(op: (B, A) => B): B = {
if (this.isEmpty) z
else tail.foldLeft(op(z, head))(op)
}
/** Stream specialization of reduceLeft which allows GC to collect
* along the way.
*/
override final def reduceLeft[B >: A](f: (B, A) => B): B = {
if (this.isEmpty) throw new UnsupportedOperationException("empty.reduceLeft")
else {
var reducedRes: B = this.head
var left = this.tail
while (!left.isEmpty) {
reducedRes = f(reducedRes, left.head)
left = left.tail
}
reducedRes
}
}
/** Returns all the elements of this stream that satisfy the
* predicate <code>p</code>. The order of the elements is preserved.
*
* @param p the predicate used to filter the stream.
* @return the elements of this stream satisfying <code>p</code>.
*/
override def partition(p: A => Boolean): (Stream[A], Stream[A]) = (filter(p(_)), filterNot(p(_)))
/** Returns a stream formed from this stream and the specified stream
* <code>that</code> by associating each element of the former with
* the element at the same position in the latter.
* If one of the two streams is longer than the other, its remaining elements are ignored.
*
* @return <code>Stream({a<sub>0</sub>,b<sub>0</sub>}, ...,
* {a<sub>min(m,n)</sub>,b<sub>min(m,n)</sub>)}</code> when
* <code>Stream(a<sub>0</sub>, ..., a<sub>m</sub>)
* zip Stream(b<sub>0</sub>, ..., b<sub>n</sub>)</code> is invoked.
*/
override final def zip[A1 >: A, B, That](that: collection.GenIterable[B])(implicit bf: CanBuildFrom[Stream[A], (A1, B), That]): That =
// we assume there is no other builder factory on streams and therefore know that That = Stream[(A1, B)]
if (isStreamBuilder(bf)) asThat(
if (this.isEmpty || that.isEmpty) Stream.Empty
else cons((this.head, that.head), asStream[(A1, B)](this.tail zip that.tail))
)
else super.zip(that)(bf)
/** Zips this iterable with its indices. `s.zipWithIndex` is equivalent to
* `s zip s.indices`
*/
override def zipWithIndex[A1 >: A, That](implicit bf: CanBuildFrom[Stream[A], (A1, Int), That]): That =
this.zip[A1, Int, That](Stream.from(0))
/** Write all defined elements of this iterable into given string builder.
* The written text begins with the string <code>start</code> and is finished by the string
* <code>end</code>. Inside, the string representations of defined elements (w.r.t.
* the method <code>toString()</code>) are separated by the string
* <code>sep</code>. The method will not force evaluation of undefined elements. A
* tail of such elements will be represented by a "?" instead.
*/
override def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder = {
def loop(pre: String, these: Stream[A]) {
if (these.isEmpty) b append end
else {
b append pre append these.head
if (these.tailDefined) loop(sep, these.tail)
else b append sep append "?" append end
}
}
b append start
loop("", this)
b
}
override def mkString(sep: String): String = mkString("", sep, "")
override def mkString: String = mkString("")
override def mkString(start: String, sep: String, end: String): String = {
this.force
super.mkString(start, sep, end)
}
override def toString = super.mkString(stringPrefix + "(", ", ", ")")
override def splitAt(n: Int): (Stream[A], Stream[A]) = (take(n), drop(n))
/** Returns the <code>n</code> first elements of this stream, or else the whole
* stream, if it has less than <code>n</code> elements.
*
* @param n the number of elements to take.
* @return the <code>n</code> first elements of this stream.
*/
override def take(n: Int): Stream[A] =
if (n <= 0 || isEmpty) Stream.empty
else if (n == 1) cons(head, Stream.empty)
else cons(head, tail take n-1)
@tailrec final override def drop(n: Int): Stream[A] =
if (n <= 0 || isEmpty) this
else tail drop n-1
/** A substream starting at index `from` and extending up to (but not including)
* index `until`.
*
* @param start The index of the first element of the returned subsequence
* @param end The index of the element following the returned subsequence
*/
override def slice(from: Int, until: Int): Stream[A] = {
val lo = from max 0
if (until <= lo || isEmpty) Stream.empty
else this drop lo take (until - lo)
}
/** The stream without its last element.
* @throws Predef.UnsupportedOperationException if the stream is empty.
*/
override def init: Stream[A] =
if (isEmpty) super.init
else if (tail.isEmpty) Stream.Empty
else cons(head, tail.init)
/** Returns the rightmost <code>n</code> elements from this iterable.
* @param n the number of elements to take
*/
override def takeRight(n: Int): Stream[A] = {
var these: Stream[A] = this
var lead = this drop n
while (!lead.isEmpty) {
these = these.tail
lead = lead.tail
}
these
}
// there's nothing we can do about dropRight, so we just keep the definition in LinearSeq
/** Returns the longest prefix of this stream whose elements satisfy
* the predicate <code>p</code>.
*
* @param p the test predicate.
*/
override def takeWhile(p: A => Boolean): Stream[A] =
if (!isEmpty && p(head)) cons(head, tail takeWhile p)
else Stream.Empty
/** Returns the longest suffix of this iterable whose first element
* does not satisfy the predicate <code>p</code>.
*
* @param p the test predicate.
*/
override def dropWhile(p: A => Boolean): Stream[A] = {
var these: Stream[A] = this
while (!these.isEmpty && p(these.head)) these = these.tail
these
}
/** Builds a new stream from this stream in which any duplicates (wrt to ==) removed.
* Among duplicate elements, only the first one is retained in the result stream
*/
override def distinct: Stream[A] =
if (isEmpty) this
else cons(head, tail.filter(head !=).distinct)
/** Returns a new sequence of given length containing the elements of this sequence followed by zero
* or more occurrences of given elements.
*/
override def padTo[B >: A, That](len: Int, elem: B)(implicit bf: CanBuildFrom[Stream[A], B, That]): That = {
def loop(len: Int, these: Stream[A]): Stream[B] =
if (these.isEmpty) Stream.fill(len)(elem)
else cons(these.head, loop(len - 1, these.tail))
if (isStreamBuilder(bf)) asThat(loop(len, this))
else super.padTo(len, elem)(bf)
}
/** A list consisting of all elements of this list in reverse order.
*/
override def reverse: Stream[A] = {
var result: Stream[A] = Stream.Empty
var these = this
while (!these.isEmpty) {
val r = Stream.consWrapper(result).#::(these.head)
r.tail // force it!
result = r
these = these.tail
}
result
}
override def flatten[B](implicit asTraversable: A => /*<:<!!!*/ TraversableOnce[B]): Stream[B] = {
def flatten1(t: Traversable[B]): Stream[B] =
if (!t.isEmpty)
cons(t.head, flatten1(t.tail))
else
tail.flatten
if (isEmpty) Stream.empty
else flatten1(asTraversable(head).toTraversable)
}
override def view = new StreamView[A, Stream[A]] {
protected lazy val underlying = self.repr
override def iterator = self.iterator
override def length = self.length
override def apply(idx: Int) = self.apply(idx)
}
/** Defines the prefix of this object's `toString` representation as `Stream`.
*/
override def stringPrefix = "Stream"
}
/** See #3273 and test case run/bug3273 for motivation. */
final class StreamIterator[+A](self: Stream[A]) extends Iterator[A] {
// A call-by-need cell.
class LazyCell(st: => Stream[A]) {
lazy val v = st
}
private var these = new LazyCell(self)
def hasNext: Boolean = these.v.nonEmpty
def next: A =
if (isEmpty) Iterator.empty.next
else {
val cur = these.v
val result = cur.head
these = new LazyCell(cur.tail)
result
}
override def toStream = {
val result = these.v
these = new LazyCell(Stream.empty)
result
}
override def toList = toStream.toList
}
/**
* The object <code>Stream</code> provides helper functions
* to manipulate streams.
*
* @author Martin Odersky, Matthias Zenger
* @version 1.1 08/08/03
* @since 2.8
*/
object Stream extends SeqFactory[Stream] {
/** The factory for streams.
* @note Methods such as map/flatMap will not invoke the Builder factory,
* but will return a new stream directly, to preserve laziness.
* The new stream is then cast to the factory's result type.
* This means that every CanBuildFrom that takes a
* Stream as its From type parameter must yield a stream as its result parameter.
* If that assumption is broken, cast errors might result.
*/
class StreamCanBuildFrom[A] extends GenericCanBuildFrom[A]
implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, Stream[A]] = new StreamCanBuildFrom[A]
/** Creates a new builder for a stream */
def newBuilder[A]: Builder[A, Stream[A]] = new StreamBuilder[A]
import scala.collection.{Iterable, Seq, IndexedSeq}
/** A builder for streams
* @note This builder is lazy only in the sense that it does not go downs the spine
* of traversables that are added as a whole. If more laziness can be achieved,
* this builder should be bypassed.
*/
class StreamBuilder[A] extends scala.collection.mutable.LazyBuilder[A, Stream[A]] {
def result: Stream[A] = parts.toStream flatMap (_.toStream)
}
object Empty extends Stream[Nothing] {
override def isEmpty = true
override def head = throw new NoSuchElementException("head of empty stream")
override def tail = throw new UnsupportedOperationException("tail of empty stream")
def tailDefined = false
}
/** The empty stream */
override def empty[A]: Stream[A] = Empty
/** A stream consisting of given elements */
override def apply[A](xs: A*): Stream[A] = xs.toStream
/** A wrapper class that adds `#::` for cons and `#:::` for concat as operations
* to streams.
*/
class ConsWrapper[A](tl: => Stream[A]) {
def #::(hd: A): Stream[A] = cons(hd, tl)
def #:::(prefix: Stream[A]): Stream[A] = prefix append tl
}
/** A wrapper method that adds `#::` for cons and `#::: for concat as operations
* to streams.
*/
implicit def consWrapper[A](stream: => Stream[A]): ConsWrapper[A] =
new ConsWrapper[A](stream)
/** An extractor that allows to pattern match streams with `#::`.
*/
object #:: {
def unapply[A](xs: Stream[A]): Option[(A, Stream[A])] =
if (xs.isEmpty) None
else Some((xs.head, xs.tail))
}
@deprecated("use #:: instead", "2.8.0")
lazy val lazy_:: = #::
/** An alternative way of building and matching Streams using Stream.cons(hd, tl).
*/
object cons {
/** A stream consisting of a given first element and remaining elements
* @param hd The first element of the result stream
* @param tl The remaining elements of the result stream
*/
def apply[A](hd: A, tl: => Stream[A]) = new Cons(hd, tl)
/** Maps a stream to its head and tail */
def unapply[A](xs: Stream[A]): Option[(A, Stream[A])] = #::.unapply(xs)
}
/** A lazy cons cell, from which streams are built. */
@SerialVersionUID(-602202424901551803L)
final class Cons[+A](hd: A, tl: => Stream[A]) extends Stream[A] with Serializable {
override def isEmpty = false
override def head = hd
@volatile private[this] var tlVal: Stream[A] = _
def tailDefined: Boolean = tlVal ne null
override def tail: Stream[A] = {
if (!tailDefined)
synchronized {
if (!tailDefined) tlVal = tl
}
tlVal
}
}
/** An infinite stream that repeatedly applies a given function to a start value.
*
* @param start the start value of the stream
* @param f the function that's repeatedly applied
* @return the stream returning the infinite sequence of values `start, f(start), f(f(start)), ...`
*/
def iterate[A](start: A)(f: A => A): Stream[A] = cons(start, iterate(f(start))(f))
override def iterate[A](start: A, len: Int)(f: A => A): Stream[A] =
iterate(start)(f) take len
/**
* Create an infinite stream starting at <code>start</code>
* and incrementing by step <code>step</code>
*
* @param start the start value of the stream
* @param step the increment value of the stream
* @return the stream starting at value <code>start</code>.
*/
def from(start: Int, step: Int): Stream[Int] =
cons(start, from(start+step, step))
/**
* Create an infinite stream starting at <code>start</code>
* and incrementing by 1.
*
* @param start the start value of the stream
* @return the stream starting at value <code>start</code>.
*/
def from(start: Int): Stream[Int] = from(start, 1)
/**
* Create an infinite stream containing the given element expression (which is computed for each
* occurrence)
*
* @param elem the element composing the resulting stream
* @return the stream containing an infinite number of elem
*/
def continually[A](elem: => A): Stream[A] = cons(elem, continually(elem))
override def fill[A](n: Int)(elem: => A): Stream[A] =
if (n <= 0) Empty else cons(elem, fill(n-1)(elem))
override def tabulate[A](n: Int)(f: Int => A): Stream[A] = {
def loop(i: Int): Stream[A] =
if (i >= n) Empty else cons(f(i), loop(i+1))
loop(0)
}
override def range[T: Integral](start: T, end: T, step: T): Stream[T] = {
val num = implicitly[Integral[T]]
import num._
if (if (step < zero) start <= end else end <= start) Empty
else cons(start, range(start + step, end, step))
}
private[immutable] def filteredTail[A](stream: Stream[A], p: A => Boolean) = {
cons(stream.head, stream.tail filter p)
}
private[immutable] def collectedTail[A, B, That](stream: Stream[A], pf: PartialFunction[A, B], bf: CanBuildFrom[Stream[A], B, That]) = {
cons(pf(stream.head), stream.tail.collect(pf)(bf).asInstanceOf[Stream[B]])
}
/** A stream containing all elements of a given iterator, in the order they are produced.
* @param it The iterator producing the stream's elements
*/
@deprecated("use it.toStream instead", "2.8.0")
def fromIterator[A](it: Iterator[A]): Stream[A] = it.toStream
/** The concatenation of a sequence of streams
*/
@deprecated("use xs.flatten instead", "2.8.0")
def concat[A](xs: Iterable[Stream[A]]): Stream[A] = concat(xs.iterator)
/** The concatenation of all streams returned by an iterator
*/
@deprecated("use xs.toStream.flatten instead", "2.8.0")
def concat[A](xs: Iterator[Stream[A]]): Stream[A] = xs.toStream.flatten //(conforms[Stream[A], scala.collection.Traversable[A]])
/**
* Create a stream with element values
* <code>v<sub>n+1</sub> = step(v<sub>n</sub>)</code>
* where <code>v<sub>0</sub> = start</code>
* and elements are in the range between <code>start</code> (inclusive)
* and <code>end</code> (exclusive)
* @param start the start value of the stream
* @param end the end value of the stream
* @param step the increment function of the stream, must be monotonically increasing or decreasing
* @return the stream starting at value <code>start</code>.
*/
@deprecated("use `iterate` instead.", "2.8.0")
def range(start: Int, end: Int, step: Int => Int): Stream[Int] =
iterate(start, end - start)(step)
/**
* Create an infinite stream containing the given element.
*
* @param elem the element composing the resulting stream
* @return the stream containing an infinite number of elem
*/
@deprecated("use `continually` instead", "2.8.0")
def const[A](elem: A): Stream[A] = cons(elem, const(elem))
/** Create a stream containing several copies of an element.
*
* @param n the length of the resulting stream
* @param elem the element composing the resulting stream
* @return the stream composed of n elements all equal to elem
*/
@deprecated("use fill(n, elem) instead", "2.8.0")
def make[A](n: Int, elem: A): Stream[A] = fill(n)(elem)
}
|