unimplicitly

unimplicitly.scala

scala> import scala.language.experimental.macros
import scala.language.experimental.macros

scala> def unimplicitlyImpl[A: c.TypeTag](c: reflect.makro.Context) = {
     |   val A = implicitly[c.TypeTag[A]].tpe
     |   val i = c.inferImplicitValue(A, silent = true)
     |   if (i == c.mirror.EmptyTree) c.reify(())
     |   else sys.error("unexpected implicit of type %s: %s".format(A, i))
     | }
unimplicitlyImpl: [A](c: scala.reflect.makro.Context)(implicit evidence$1: c.TypeTag[A])c.mirror.Expr[Unit]

scala> def unimplicitly[A] = macro unimplicitlyImpl[A]
unimplicitly: [A]=> Unit

scala> unimplicitly[String]

scala> unimplicitly[Int => Int]
<console>:11: error: exception during macro expansion: 
java.lang.RuntimeException: unexpected implicit of type Int => Int: scala.this.Predef.conforms[Int]
	at scala.sys.package$.error(package.scala:27)
	at .m(<console>:11)

              unimplicitly[Int => Int]
                          ^

Ah thanks... my REPL cut-n-pastery wasn't up to scratch, thanks to the crashy tab completion for SIP-18.

scala> import language.expReplGlobal.abort: no-symbol does not have an owner (this is a bug: scala version 2.10.0-20120420-170445-56c1f29250)
error: no-symbol does not have an owner (this is a bug: scala version 2.10.0-20120420-170445-56c1f29250)
sac
<console>:7: error: value expsac is not a member of object language
       import language.expsac

Heh, with a dash of intentional ambiguity macros aren't needed at all: http://paste.pocoo.org/show/584923/

You do know you can edit (and version) your gists, don't you?