Error "Macro has not been expanded" when using monadic Nothing #41
Description
In monadic[F] { ... }, if each is applied to a monad of type F[Nothing], a compilation error "Macro has not been expanded" occurs.
F[Nothing] is a natural type for a fail operation (e.g., Nil, None) in a monad, since the return value can be upcast to anything (e.g., val x = if (x >= 0) sqrt(x) else None.each would be a use case).
Example code:
object MonadicNeedsCast {
def main(args: Array[String]): Unit = {
val monad = monadic[Option] {
None.each // Normally, this would be inside an if and represent a failure of the computation
// (None:Option[Unit]).each // This one works
55
}
println(monad) // Should be None
}
}
The error also appears with monadic[List] or with custom monads. It also appears when using fail.each where fail has type [T]fail( => T).
I am using Scala 2.11.8 and Each 2.0.0.