From 8e64bed3c2b61f90ceb6dfdfaf080bab627c63d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9D=A8=E5=8D=9A=20=28Yang=20Bo=29?= <pop.atry@gmail.com>
Date: Fri, 21 Apr 2017 19:54:52 +0800
Subject: [PATCH] Add bindFirst and curried methods for Poly

---
 core/src/main/scala/shapeless/poly.scala | 60 ++++++++++++++++++++++++
 core/src/test/scala/shapeless/poly.scala | 34 ++++++++++++++
 2 files changed, 94 insertions(+)

diff --git a/core/src/main/scala/shapeless/poly.scala b/core/src/main/scala/shapeless/poly.scala
index b5a350617..6dae66e96 100644
--- a/core/src/main/scala/shapeless/poly.scala
+++ b/core/src/main/scala/shapeless/poly.scala
@@ -113,6 +113,59 @@ object PolyDefns extends Cases {
       }
   }
 
+  final case class BindFirst[F, Head](head: Head) extends Poly
+
+  object BindFirst {
+    implicit def bindFirstCase[BF, F, Head, Tail <: HList, Result0](
+        implicit
+        unpack2: BF <:< BindFirst[F, Head],
+        witnessBF: Witness.Aux[BF],
+        finalCall: Case.Aux[F, Head :: Tail, Result0]
+    ): Case.Aux[BF, Tail, Result0] = new Case[BF, Tail] {
+      type Result = Result0
+      val value: Tail => Result = { tail: Tail =>
+        finalCall.value(witnessBF.value.head :: tail)
+      }
+    }
+  }
+
+  final case class Curried[F, ParameterAccumulator <: HList](parameters: ParameterAccumulator) extends Poly1
+
+  private[PolyDefns] sealed trait LowPriorityCurried {
+    implicit def partialApplied[
+      Self,
+      F,
+      ParameterAccumulator <: HList,
+      CurrentParameter,
+      AllParameters <: HList,
+      RestParameters <: HList,
+      CurrentLength <: Nat
+    ](implicit
+      constraint: Self <:< Curried[F, ParameterAccumulator],
+      witnessSelf: Witness.Aux[Self],
+      finalCall: Case[F, AllParameters],
+      length: ops.hlist.Length.Aux[CurrentParameter :: ParameterAccumulator, CurrentLength],
+      reverseSplit: ops.hlist.ReverseSplit.Aux[AllParameters, CurrentLength, CurrentParameter :: ParameterAccumulator, RestParameters],
+      hasRestParameters: RestParameters <:< (_ :: _)
+    ): Case1.Aux[Self, CurrentParameter, Curried[F, CurrentParameter :: ParameterAccumulator]] = Case1 {
+      nextParameter: CurrentParameter =>
+        Curried[F, CurrentParameter :: ParameterAccumulator](nextParameter :: witnessSelf.value.parameters)
+    }
+  }
+
+  object Curried extends LowPriorityCurried {
+    implicit def lastParameter[Self, F, LastParameter, ParameterAccumulator <: HList, AllParameters <: HList, Result0](
+        implicit
+        constraint: Self <:< Curried[F, ParameterAccumulator],
+        witnessSelf: Witness.Aux[Self],
+        reverse: ops.hlist.Reverse.Aux[LastParameter :: ParameterAccumulator, AllParameters],
+        finalCall: Case.Aux[F, AllParameters, Result0]
+    ): Case1.Aux[Self, LastParameter, Result0] = Case1 {
+      lastParameter: LastParameter =>
+        finalCall(reverse(lastParameter :: witnessSelf.value.parameters))
+    }
+  }
+
   /**
    * Base class for lifting a `Function1` to a `Poly1`
    */
@@ -246,6 +299,13 @@ trait Poly extends PolyApply with Serializable {
  */
 object Poly extends PolyInst {
   implicit def inst0(p: Poly)(implicit cse : p.ProductCase[HNil]) : cse.Result = cse()
+
+  import PolyDefns._
+  
+  final def bindFirst[Head](p: Poly, head: Head): BindFirst[p.type, Head] = new BindFirst[p.type, Head](head)
+
+  final def curried(p: Poly): Curried[p.type, HNil] = new Curried[p.type, HNil](HNil)
+
 }
 
 /**
diff --git a/core/src/test/scala/shapeless/poly.scala b/core/src/test/scala/shapeless/poly.scala
index f385414fc..01b853351 100644
--- a/core/src/test/scala/shapeless/poly.scala
+++ b/core/src/test/scala/shapeless/poly.scala
@@ -439,4 +439,38 @@ class PolyTests {
 
     assertTypedEquals[Int](16, r)
   }
+
+  @Test
+  def testBindFirst: Unit = {
+    object p extends Poly3 {
+      implicit def x = at[Int, String, Double] { (i, s, d) =>
+        s"$i, $d, $s"
+      }
+    }
+
+    val bf = Poly.bindFirst(p, 2)
+    val r = bf("bar", 3.5)
+    assertTypedEquals[String]("2, 3.5, bar", r)
+
+    val l = 1.0 :: 2.0 :: 3.0 :: HNil
+    assertTypedEquals[String]("2, 3.0, 2, 2.0, 2, 1.0, x", l.foldLeft("x")(bf))
+  }
+
+  @Test
+  def testCurried: Unit = {
+    object p extends Poly3 {
+      implicit def x = at[Int, Double, String] { (i, d, s) =>
+        s"$i, $d, $s"
+      }
+    }
+
+    val c = Poly.curried(p)
+    val c1 = c(1)
+    val c2 = c1(42.5)
+    val r = c2("foo")
+    assertTypedEquals[String]("1, 42.5, foo", r)
+
+    val l = "x" :: "y" :: "z" :: HNil
+    assertEquals("1, 42.5, x" :: "1, 42.5, y" :: "1, 42.5, z" :: HNil, l.map(c2))
+  }
 }