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Add tests to cover derived methods leftMap and rightMap on BiFunctor #652

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Nov 15, 2015
Merged

Add tests to cover derived methods leftMap and rightMap on BiFunctor #652

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b86d739
Add tests to cover derived methods leftMap and rightMap
mikejcurry Nov 15, 2015
d744871
Add leftMap and rightMap to syntax and add associativity tests for le…
mikejcurry Nov 15, 2015
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5 changes: 5 additions & 0 deletions core/src/main/scala/cats/syntax/bifunctor.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -10,5 +10,10 @@ trait BifunctorSyntax {
}

class BifunctorOps[F[_, _], A, B](fab: F[A, B])(implicit F: Bifunctor[F]) {

def bimap[C, D](f: A => C, g: B => D): F[C,D] = F.bimap(fab)(f,g)

def leftMap[C](f: A => C): F[C, B] = F.leftMap(fab)(f)

def rightMap[D](f: B => D): F[A, D] = F.rightMap(fab)(f)
}
15 changes: 15 additions & 0 deletions laws/src/main/scala/cats/laws/BifunctorLaws.scala
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Expand Up @@ -15,6 +15,21 @@ trait BifunctorLaws[F[_, _]] {
def bifunctorComposition[A, B, C, X, Y, Z](fa: F[A, X], f: A => B, f2: B => C, g: X => Y, g2: Y => Z): IsEq[F[C, Z]] = {
fa.bimap(f, g).bimap(f2, g2) <-> fa.bimap(f andThen f2, g andThen g2)
}

def bifunctorLeftMapIdentity[A, B](fa: F[A, B]): IsEq[F[A, B]] =
fa.leftMap(identity) <-> fa

def bifunctorRightMapIdentity[A, B](fa: F[A, B]): IsEq[F[A, B]] =
fa.rightMap(identity) <-> fa

def bifunctorLeftMapComposition[A, B, C, D](fa: F[A, B], f: A => C, g: C => D): IsEq[F[D, B]] = {
fa.leftMap(f).leftMap(g) <-> fa.leftMap(f andThen g)
}

def bifunctorRightMapComposition[A, B, C, D](fa: F[A, B], f: B => C, g: C => D): IsEq[F[A, D]] = {
fa.rightMap(f).rightMap(g) <-> fa.rightMap(f andThen g)
}

}

object BifunctorLaws {
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10 changes: 8 additions & 2 deletions laws/src/main/scala/cats/laws/discipline/BifunctorTests.scala
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Expand Up @@ -17,13 +17,19 @@ trait BifunctorTests[F[_, _]] extends Laws {
ArbB2: Arbitrary[B => B2],
ArbB3: Arbitrary[B2 => B3],
EqFAB: Eq[F[A, B]],
EqFCZ: Eq[F[A3, B3]]
EqFCZ: Eq[F[A3, B3]],
EqFA3B: Eq[F[A3, B]],
EqFAB3: Eq[F[A, B3]]
): RuleSet = {
new DefaultRuleSet(
name = "Bifunctor",
parent = None,
"Bifunctor Identity" -> forAll(laws.bifunctorIdentity[A, B] _),
"Bifunctor associativity" -> forAll(laws.bifunctorComposition[A, A2, A3, B, B2, B3] _)
"Bifunctor associativity" -> forAll(laws.bifunctorComposition[A, A2, A3, B, B2, B3] _),
"Bifunctor leftMap Identity" -> forAll(laws.bifunctorLeftMapIdentity[A, B] _),
"Bifunctor rightMap Identity" -> forAll(laws.bifunctorRightMapIdentity[A, B] _),
"Bifunctor leftMap associativity" -> forAll(laws.bifunctorLeftMapComposition[A, B, A2, A3] _),
"Bifunctor rightMap associativity" -> forAll(laws.bifunctorRightMapComposition[A, B, B2, B3] _)
)
}
}
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