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Add more syntax #1398

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merged 4 commits into from
Oct 18, 2016
+15 −1
Merged

Add more syntax #1398

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0decc57
Add compose aliases
Fristi Sep 30, 2016
7808344
Alter compose syntax so it doesn't cause problems with right associat…
Fristi Oct 1, 2016
996b5bb
Fix compile issues
Fristi Oct 1, 2016
13209e7
Seems operator associativity works?
Fristi Oct 18, 2016
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3 changes: 3 additions & 0 deletions core/src/main/scala/cats/arrow/Compose.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -7,8 +7,11 @@ import simulacrum.typeclass
* Must obey the laws defined in cats.laws.ComposeLaws.
*/
@typeclass trait Compose[F[_, _]] { self =>

@simulacrum.op(":<<", alias = true)
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I don't like the asymmetry here. If we have the :<< The other should be >>:.

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@Fristi Fristi Oct 14, 2016 •
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I also dislike it, but I am getting this compile error when introducing >>:, guess it's right associative, even when you put the : on the right.

[error] /Users/mark/Projects/cats/tests/src/test/scala/cats/tests/SyntaxTests.scala:55: type mismatch;
[error]  found   : x$1.type (with underlying type F[B,C])
[error]  required: F[D,?]
[error]     val a = x >>: y >>: z
[error]

def compose[A, B, C](f: F[B, C], g: F[A, B]): F[A, C]

@simulacrum.op(">>>", alias = true)
def andThen[A, B, C](f: F[A, B], g: F[B, C]): F[A, C] =
compose(g, f)

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13 changes: 12 additions & 1 deletion tests/src/test/scala/cats/tests/SyntaxTests.scala
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Original file line number Diff line number Diff line change
@@ -1,9 +1,10 @@
package cats
package tests

import cats.arrow.Compose
import cats.instances.AllInstances
import cats.syntax.AllSyntax
import cats.functor.{Invariant, Contravariant}
import cats.functor.{Contravariant, Invariant}

/**
* Test that our syntax implicits are working.
Expand Down Expand Up @@ -46,6 +47,16 @@ object SyntaxTests extends AllInstances with AllSyntax {
val z: Boolean = x.isEmpty
}

def testCompose[F[_,_] : Compose, A, B, C, D]: Unit = {
val x = mock[F[A, B]]
val y = mock[F[B, C]]
val z = mock[F[C, D]]

val a = x >>> y >>> z
val b = z :<< y :<< x

}

def testEq[A: Eq]: Unit = {
val x = mock[A]
val y = mock[A]
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