SystemFw · October 9, 2017 23:20 · Oct 9, 2017
diff --git a/Q.scala b/Q.scala
@@ -0,0 +1,51 @@
+
+object Q {
+  import shapeless._, labelled._, ops.record.Selector
+
+  trait Accessors[T, I] {
+    type Out
+    def value: Out
+  }
+  object Accessors {
+    type Aux[T, I, O] = Accessors[T, I] { type Out = O }
+
+    class Curry[T] {
+      def get[L](implicit ev: LabelledGeneric.Aux[T, L],
+                 a: Accessors[T, L]): a.Out =
+        a.value
+    }
+
+    def of[T] = new Curry[T]
+
+    def instance[T, I, O](body: O): Accessors.Aux[T, I, O] =
+      new Accessors[T, I] {
+        type Out = O
+        def value = body
+      }
+
+    implicit def hnil[T]: Accessors.Aux[T, HNil, HNil] = instance(HNil)
+
+    implicit def kv[T, K <: Symbol, V, R <: HList, R1 <: HList](
+        implicit accessor: Accessor[T, K],
+        next: Accessors.Aux[T, R, R1])
+      : Accessors.Aux[T, FieldType[K, V] :: R, (T => accessor.Out) :: R1] =
+      instance(accessor.get :: next.value)
+
+    trait Accessor[T, K] {
+      type Out
+      def get: T => Out
+    }
+
+    object Accessor {
+      type Aux[T, K, O] = Accessor[T, K] { type Out = O }
+
+      implicit def all[T, K <: Symbol, L <: HList, O](
+          implicit gen: LabelledGeneric.Aux[T, L],
+          select: Selector.Aux[L, K, O]): Accessor.Aux[T, K, O] =
+        new Accessor[T, K] {
+          type Out = O
+          def get: T => Out = t => select(gen.to(t))
+        }
+    }
+  }
+}
diff --git a/Test.scala b/Test.scala
@@ -0,0 +1,13 @@
+object Test {
+  import shapeless._
+  import Q._
+
+  case class Foo(a: Int, b: String)
+  val foo = Foo(1, "yo")
+
+  def accessors = Accessors.of[Foo].get
+
+  val wellTypes: (Foo => Int) :: (Foo => String) :: HNil = accessors
+  val a = accessors.head.apply(foo) //1
+  val b = accessors.tail.head.apply(foo) //yo
+}
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