Updated FunctionK.lift as per typelevel#2553 (comment)

drdozer · Mar 29, 2019 · 2d4cc2c · 2d4cc2c
1 parent 355979e
commit 2d4cc2c
Showing 1 changed file with 5 additions and 66 deletions.
diff --git a/core/src/main/scala/cats/arrow/FunctionK.scala b/core/src/main/scala/cats/arrow/FunctionK.scala
@@ -3,8 +3,6 @@ package arrow
 
 import cats.data.Coproduct
 
-import cats.macros.MacroCompat
-
 /**
   * `FunctionK[F[_], G[_]]` is a functor transformation from `F` to `G`
   * in the same manner that function `A => B` is a morphism from values
@@ -80,73 +78,14 @@ object FunctionK {
     *
     * Additionally, the type parameters on `f` must not be specified.
     */
-  def lift[F[_], G[_]](f: (F[α] ⇒ G[α]) forSome { type α }): FunctionK[F, G] =
-    macro FunctionKMacros.lift[F, G]
-
-}
-
-private[arrow] object FunctionKMacros extends MacroCompat {
-
-  def lift[F[_], G[_]](c: Context)(
-    f: c.Expr[(F[α] ⇒ G[α]) forSome { type α }]
-  )(
-    implicit evF: c.WeakTypeTag[F[_]], evG: c.WeakTypeTag[G[_]]
-  ): c.Expr[FunctionK[F, G]] =
-    c.Expr[FunctionK[F, G]](new Lifter[c.type ](c).lift[F, G](f.tree))
-    // ^^note: extra space after c.type to appease scalastyle
-
-  private[this] class Lifter[C <: Context](val c: C) {
-    import c.universe._
-
-    def lift[F[_], G[_]](tree: Tree)(
-      implicit evF: c.WeakTypeTag[F[_]], evG: c.WeakTypeTag[G[_]]
-    ): Tree = unblock(tree) match {
-      case q"($param) => $trans[..$typeArgs](${ arg: Ident })" if param.name == arg.name ⇒
+  def lift[F[_]]: LiftPartiallyApplied[F] = new LiftPartiallyApplied
 
-        typeArgs
-          .collect { case tt: TypeTree => tt }
-          .find(tt => Option(tt.original).isDefined)
-          .foreach { param => c.abort(param.pos,
-            s"type parameter $param must not be supplied when lifting function $trans to FunctionK")
-        }
+  private[arrow] final class LiftPartiallyApplied[F[_]](val dummy: Boolean = true) extends AnyVal {
+    type T
 
-        val F = punchHole(evF.tpe)
-        val G = punchHole(evG.tpe)
-
-        q"""
-        new FunctionK[$F, $G] {
-          def apply[A](fa: $F[A]): $G[A] = $trans(fa)
-        }
-       """
-      case other ⇒
-        c.abort(other.pos, s"Unexpected tree $other when lifting to FunctionK")
-    }
-
-    private[this] def unblock(tree: Tree): Tree = tree match {
-      case Block(Nil, expr) ⇒ expr
-      case _                ⇒ tree
+    def apply[G[_]](f: F[T] => G[T]): FunctionK[F, G] = new FunctionK[F, G] {
+      def apply[A](fa: F[A]): G[A] = f(fa.asInstanceOf[F[T]]).asInstanceOf[G[A]]
     }
-
-    private[this] def punchHole(tpe: Type): Tree = tpe match {
-      case PolyType(undet :: Nil, underlying: TypeRef) ⇒
-        val α = compatNewTypeName(c, "α")
-        def rebind(typeRef: TypeRef): Tree =
-          if (typeRef.sym == undet) tq"$α"
-          else {
-            val args = typeRef.args.map {
-              case ref: TypeRef => rebind(ref)
-              case arg => tq"$arg"
-            }
-            tq"${typeRef.sym}[..$args]"
-          }
-        val rebound = rebind(underlying)
-        tq"""({type λ[$α] = $rebound})#λ"""
-      case TypeRef(pre, sym, Nil) ⇒
-        tq"$sym"
-      case _ =>
-        c.abort(c.enclosingPosition, s"Unexpected type $tpe when lifting to FunctionK")
-    }
-
   }
 
 }