Fun with fun-deps in scala.

fun-deps.scala

/*
object Test0 {
  import scalaz.meta.Foo._
  val s: String = 1024.bar
  val i: Int = "test".bar

  println(s) // bar
  println(i) // 42
}
*/

import language.experimental.macros
import scala.reflect.macros.whitebox.Context
import scala.language.implicitConversions

object Foo {
  implicit def fooOps[I, O](i: I)(implicit I: Foo[I, O]): Foo[I, O] = I
  implicit def foo[I, O]: Foo[I, O] = macro FooMacros.foo[I, O]
}

class Foo[I, O] {
  final def bar: O = macro FooMacros.bar[I, O]
}

object FooMacros {

  def foo[I: c.WeakTypeTag, O: c.WeakTypeTag](c: Context): c.Expr[Foo[I, O]] = {
    import c.universe._
    val i = weakTypeOf[I]
    val o = if (i =:= typeOf[String]) {
      typeOf[Int]
    } else {
      typeOf[String]
    }
    c.Expr[Foo[I, O]](q"new scalaz.meta.Foo[$i, $o]")
  }

  def bar[I: c.WeakTypeTag, O: c.WeakTypeTag](c: Context): c.Expr[O] = {
    import c.universe._
    val Apply(Apply(_, List(tree)), _) = c.prefix.tree
    if (weakTypeOf[O] =:= typeOf[Int]) {
      c.Expr[O](q"42")
    } else {
      c.Expr[O](q""""bar"""")
    }
  }
}