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foldLeft, foldRight, other Foldable specializations #11592

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merged 7 commits into from
Nov 9, 2021
Merged

foldLeft, foldRight, other Foldable specializations #11592

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d574ae0
FoldableContravariant, a mapping for Foldable instances
S11001001 Nov 9, 2021
982b3a1
use FoldableContravariant to specialize several ImmArraySeq, NonEmpty…
S11001001 Nov 9, 2021
77bf107
folding specializations for ImmArray
S11001001 Nov 9, 2021
962513a
a few docs for FoldableContravariant
S11001001 Nov 9, 2021
7f0a5d9
specializations for FrontStack
S11001001 Nov 9, 2021
857ece6
no changelog
S11001001 Nov 9, 2021
f8821be
Merge commit '6372d41d1302b3d294c3ea99095e920fc4c6ef28' into foldLeft…
S11001001 Nov 9, 2021
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a few docs for FoldableContravariant
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@S11001001
S11001001 committed Nov 9, 2021
commit 962513aec2b460cc361b75724b066aa196d8e30f
6 changes: 6 additions & 0 deletions libs-scala/scala-utils/src/main/scala/com/daml/scalautil/FoldableContravariant.scala
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Expand Up @@ -7,6 +7,8 @@ import scalaz.{Monoid, Foldable, Semigroup}
import FoldableContravariant._

// Specialized overrides for when a Foldable wraps another Foldable.
// If you need to hand-write some of these, just mix in the traits you
// don't want to hand-write.
private[daml] trait FoldableContravariant[X[_], Y[_]]
extends CoreOps[X, Y]
with Semigroupoids[X, Y]
Expand All @@ -19,13 +21,15 @@ private[daml] object FoldableContravariant {
protected[this] def ctmap[A](ax: X[A]): Y[A]
}

// non-derived combinators
trait CoreOps[X[_], Y[_]] extends Foldable[X] with CtMap[X, Y] {
override final def foldLeft[A, B](xa: X[A], z: B)(f: (B, A) => B) = Y.foldLeft(ctmap(xa), z)(f)
override final def foldRight[A, B](xa: X[A], z: => B)(f: (A, => B) => B) =
Y.foldRight(ctmap(xa), z)(f)
override final def foldMap[A, Z: Monoid](xa: X[A])(f: A => Z) = Y.foldMap(ctmap(xa))(f)
}

// plays on functions from the semigroupoids library
trait Semigroupoids[X[_], Y[_]] extends Foldable[X] with CtMap[X, Y] {
override final def foldMapRight1Opt[A, B](xa: X[A])(z: A => B)(f: (A, B) => B) =
Y.foldMapRight1Opt(ctmap(xa))(z)(f)
Expand All @@ -35,6 +39,7 @@ private[daml] object FoldableContravariant {
Y.foldMap1Opt(ctmap(xa))(f)
}

// to (collection type) converters
trait Conversions[X[_], Y[_]] extends Foldable[X] with CtMap[X, Y] {
override final def toStream[A](xa: X[A]) = Y.toStream(ctmap(xa))
override final def toSet[A](xa: X[A]) = Y.toSet(ctmap(xa))
Expand All @@ -45,6 +50,7 @@ private[daml] object FoldableContravariant {
Y.toEphemeralStream(ctmap(xa))
}

// list-like operations
trait Lookups[X[_], Y[_]] extends Foldable[X] with CtMap[X, Y] {
override final def index[A](xa: X[A], i: Int) = Y.index(ctmap(xa), i)
override final def length[A](xa: X[A]) = Y.length(ctmap(xa))
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