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Better Chain Arbitrary #2420

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Aug 18, 2018
Merged

Better Chain Arbitrary #2420

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705a658
Better Chain Arbitrary
Aug 17, 2018
f8ee6cf
Fix bug in uncons
Aug 18, 2018
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23 changes: 5 additions & 18 deletions core/src/main/scala/cats/data/Chain.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -31,8 +31,10 @@ sealed abstract class Chain[+A] {
result = Some(a -> next)
case Append(l, r) => c = l; rights += r
case Wrap(seq) =>
val tail = seq.tail
val next = fromSeq(tail)
val tail = fromSeq(seq.tail)
val next =
if (rights.isEmpty) tail
else tail ++ rights.reduceLeft((x, y) => Append(y, x))
result = Some((seq.head, next))
case Empty =>
if (rights.isEmpty) {
Expand Down Expand Up @@ -424,22 +426,7 @@ object Chain extends ChainInstances {

/** Creates a Chain from the specified elements. */
def apply[A](as: A*): Chain[A] =
as match {
case w: collection.mutable.WrappedArray[A] =>
if (w.isEmpty) nil
else if (w.size == 1) one(w.head)
else {
val arr: Array[A] = w.array
var c: Chain[A] = one(arr.last)
var idx = arr.size - 2
while (idx >= 0) {
c = Append(one(arr(idx)), c)
idx -= 1
}
c
}
case _ => fromSeq(as)
}
fromSeq(as)

// scalastyle:off null
class ChainIterator[A](self: Chain[A]) extends Iterator[A] {
Expand Down
17 changes: 14 additions & 3 deletions laws/src/main/scala/cats/laws/discipline/Arbitrary.scala
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Expand Up @@ -293,9 +293,20 @@ object arbitrary extends ArbitraryInstances0 {
case 1 => A.arbitrary.map(Chain.one)
case 2 => A.arbitrary.flatMap(a1 => A.arbitrary.flatMap(a2 =>
Chain.concat(Chain.one(a1), Chain.one(a2))))
case n => Chain.fromSeq(Range.apply(0, n)).foldLeft(Gen.const(Chain.empty[A])) { (gen, _) =>
gen.flatMap(cat => A.arbitrary.map(a => cat :+ a))
}
case n =>
def fromList(m: Int) = Range.apply(0, m).toList.foldLeft(Gen.const(List.empty[A])) { (gen, _) =>
gen.flatMap(list => A.arbitrary.map(_ :: list))
}.map(Chain.fromSeq)
val split = fromList(n / 2).flatMap(as => fromList(n / 2).map(_ ++ as))
val appended = fromList(n - 1).flatMap(as => A.arbitrary.map(as :+ _))
val prepended = fromList(n - 1).flatMap(as => A.arbitrary.map(_ +: as))
val startEnd = fromList(n - 2).flatMap(as => A.arbitrary.flatMap(a => A.arbitrary.map(_ +: (as :+ a))))
val betweenListsAndEnd = fromList((n - 1) / 2).flatMap(as => A.arbitrary.flatMap(a =>
fromList((n - 1) / 2).flatMap(as2 => A.arbitrary.map(a2 => (as2 ++ (a +: as)) :+ a2))))
val betweenListsAndFront = fromList((n - 1) / 2).flatMap(as => A.arbitrary.flatMap(a =>
fromList((n - 1) / 2).flatMap(as2 => A.arbitrary.map(a2 => a2 +: (as2 ++ (a +: as))))))
Gen.oneOf(fromList(n), split, appended, prepended, startEnd, betweenListsAndEnd, betweenListsAndFront)

})

implicit def catsLawsCogenForChain[A](implicit A: Cogen[A]): Cogen[Chain[A]] =
Expand Down