Merge pull request #49 from mikejcurry/add-imp-support

Use imp summon macro to summon type class instance for apply

build.sbt

@@ -34,7 +34,8 @@ lazy val commonSettings = Seq(
     Resolver.sonatypeRepo("snapshots")
   ),
   libraryDependencies ++= Seq(
-    "org.scalatest" %%% "scalatest" % "3.0.0-M7" % "test"
+    "org.scalatest" %%% "scalatest" % "3.0.0-M7" % "test",
+    "org.spire-math" %% "imp" % "0.2.0"
   ),
   addCompilerPlugin("org.scalamacros" %% "paradise" % "2.1.0" cross CrossVersion.full),
   licenses += ("Three-clause BSD-style", url("https://github.com/mpilquist/simulacrum/blob/master/LICENSE")),
@@ -144,4 +145,3 @@ lazy val noPublishSettings = Seq(
   publishLocal := (),
   publishArtifact := false
 )
-

core/src/main/scala/simulacrum/typeclass.scala

@@ -6,6 +6,7 @@ import scala.reflect.macros.whitebox.Context
 
 import macrocompat._
 
+
 /**
  * Annotation that may be applied to methods on a type that is annotated with `@typeclass`.
  *
@@ -298,7 +299,17 @@ class TypeClassMacros(val c: Context) {
 
     def generateCompanion(typeClass: ClassDef, tparam0: TypeDef, proper: Boolean, comp: Tree) = {
       val tparam = eliminateVariance(tparam0)
-      val summoner = q"def apply[$tparam](implicit instance: ${typeClass.name}[${tparam.name}]): ${typeClass.name}[${tparam.name}] = instance"
+
+      // The apply method uses the imp macro to summon the appropriate instance, but as imp is a
+      // macro itself, an import is required in the generated tree to allow the macro to be called
+      // in the generated tree.
+      val summonerImports = q"""
+        import scala.language.experimental.macros
+        """
+
+      val summoner = q"""
+        def apply[$tparam](implicit ev: ${typeClass.name}[${tparam.name}]): ${typeClass.name}[${tparam.name}] =
+          macro imp.summon[${typeClass.name}[${tparam.name}]]"""
 
       val liftedTypeArg = if (proper) None else Some {
         // We have a TypeClass[F[_ >: L <: U]], so let's create a F[X >: L <: U] for a fresh name X
@@ -359,6 +370,7 @@ class TypeClassMacros(val c: Context) {
       val companion = q"""
         $mods object $name extends ..$bases {
           ..$body
+          $summonerImports
           $summoner
           ..$opsMembers
         }