macro with computed return type

macro-ret.scala

scala> def retImpl(c: Context)(b: c.Expr[Boolean]): c.Expr[Any] = {
     |    import c.universe._
     |   val Literal(Constant(bool: Boolean)) = b.tree
     |   if (bool) c.reify(0) else c.reify(false)
     | }
retImpl: (c: scala.reflect.makro.Context)(b: c.Expr[Boolean])c.Expr[Any]

scala> def ret(b: Boolean) = macro retImpl
ret: (b: Boolean)Any

scala> ret(true)
res3: Int = 0

scala> ret(false)
res4: Boolean = false

scala> ret(false) | true
res5: Boolean = true

scala> ret(false) * 1
<console>:16: error: value * is not a member of Boolean
              ret(false) * 1
                         ^

scala> ret(true) * 1
res7: Int = 0

val x = true
ret(x) // --> match error

In other words, compile time assertions will probably need to be restricted to a few tree patterns such as literals...