ScalaColliderMacroRateChecking.scala

ScalaColliderMacroRateChecking.scala

// for Scala 2.10.0-M4
import language.experimental.macros
import import scala.reflect.makro._

// ScalaCollider skeleton
sealed trait MaybeRate
object UndefinedRate extends MaybeRate
sealed trait Rate extends MaybeRate
object audio extends Rate
object control extends Rate
trait GE { def rate: MaybeRate }

// Shamelessly stolen from Jason Zaugg (https://github.com/retronym/macrocosm)
def assert1Impl(c: Context)(cond: c.Expr[Boolean]) = {
   import c.universe._
   val condCode = c.Expr[String](Literal(Constant(show(cond.tree))))
   c.reify {
      assert(cond.splice, condCode.splice)
      ()
   }
}
def assert1(cond: Boolean): Unit = macro assert1Impl

// Crash test dummies
object WhiteNoiseAr extends GE { def rate = audio }
object LFNoiseKr extends GE { def rate = control }
object UnknownGE extends GE { def rate = UndefinedRate }

// Test enhanced graph element
object LPF {
   def ar( in: GE ) : LPF = {
      assert1( in.rate == UndefinedRate || in.rate == audio )
      apply( audio, in )
   }
}
case class LPF( rate: Rate, in: GE )

//// Tests (uncomment/eval each)
// LPF.ar( WhiteNoiseAr ) // compiles
// LPF.ar( UnknownGE )    // compiles (might throw a runtime exception later)
// LPF.ar( LFNoiseKr )    // won't compile

That still only gives runtime checks. What is needed is rather def ar(in: GE) : LPF = macro arImpl(in)