Add more syntax (#1398)

* Add compose aliases

* Alter compose syntax so it doesn't cause problems with right associative statements

* Fix compile issues

* Seems operator associativity works?

core/src/main/scala/cats/arrow/Compose.scala

@@ -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)
   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)
 

tests/src/test/scala/cats/tests/SyntaxTests.scala

@@ -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.
@@ -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]