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Improve merging of Char parsers #291

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merged 2 commits into from
Nov 3, 2021
Merged

Improve merging of Char parsers #291

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2aedc17
Improve merging of Char parsers
johnynek Oct 30, 2021
f1a3422
take suggestion from regadas on pattern match change
johnynek Nov 1, 2021
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2 changes: 1 addition & 1 deletion core/js/src/main/scala/cats/parse/BitSet.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,6 @@ object BitSetUtil {
def toIter(m: Int, bs: BitSet): Iterator[Char] =
bs.iterator.map { i => (i + m).toChar } ++ Iterator.single(m.toChar)

bs.flatMap { case (m, bs) => toIter(m, bs) }
bs.iterator.flatMap { case (m, bs) => toIter(m, bs) }.toSet
}
}
2 changes: 1 addition & 1 deletion core/jvm/src/main/scala/cats/parse/BitSet.scala
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Expand Up @@ -56,6 +56,6 @@ object BitSetUtil {
.takeWhile(_ >= 0)
.map { i => (m + i).toChar }

bs.flatMap { case (m, bs) => toIter(m, bs) }
bs.iterator.flatMap { case (m, bs) => toIter(m, bs) }.toSet
}
}
16 changes: 11 additions & 5 deletions core/shared/src/main/scala/cats/parse/Parser.scala
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Expand Up @@ -2603,11 +2603,17 @@ object Parser {
*/
def mergeCharIn[A, P0 <: Parser0[A]](ps: List[P0]): List[P0] = {
@annotation.tailrec
def loop(ps: List[P0], front: List[(Int, BitSetUtil.Tpe)], result: Chain[P0]): Chain[P0] = {
def loop(ps: List[P0], front: List[CharIn], result: Chain[P0]): Chain[P0] = {
@inline
def frontRes: Chain[P0] =
if (front.isEmpty) Chain.nil
else Chain.one(Parser.charIn(BitSetUtil.union(front)).asInstanceOf[P0])
front match {
case Nil => Chain.nil
case one :: Nil => Chain.one(one.asInstanceOf[P0])
case many =>
// we need to union
val minBs: List[(Int, BitSetUtil.Tpe)] = many.map { case CharIn(m, bs, _) => (m, bs) }
Chain.one(Parser.charIn(BitSetUtil.union(minBs)).asInstanceOf[P0])
Comment on lines +2614 to +2615
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could we have a version of union with Iterator and avoid the copy in minBs?

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we certainly could. I wasn't sure it was worth it because we already iterate through the number of parsers regularly, but the characters inside the parsers (which we have to iterate when allocating a new CharIn to compute the ranges) could be more expensive, which was what I was targeting here.

Do you want me to address this before merging?

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We can address this as a follow-up for sure!

}

ps match {
case Nil => result ++ frontRes
Expand All @@ -2616,8 +2622,8 @@ object Parser {
// and any direct prefix CharIns
val tail1 = tail.filterNot(_.isInstanceOf[CharIn])
(result :+ AnyChar.asInstanceOf[P0]) ++ Chain.fromSeq(tail1)
case CharIn(m, bs, _) :: tail =>
loop(tail, (m, bs) :: front, result)
case (ci: CharIn) :: tail =>
loop(tail, ci :: front, result)
case h :: tail =>
// h is not an AnyChar or CharIn
// we make our prefix frontRes
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