I am writing an interpreter and tried to use solution from how-to-set-up-implicit-conversion-to-allow-arithmetic-between-numeric-types for the same problem I need to be able to add Boolean + Boolean, Int + Boolean, Boolean + Int, Int + Double, Double + Double etc.
So I used WeakConformance and C classes from that solution
sealed trait WeakConformance[A <: AnyVal, B <: AnyVal, C] {
implicit def aToC(a: A): C
implicit def bToC(b: B): C
}
object WeakConformance {
implicit def SameSame[T <: AnyVal]: WeakConformance[T, T, T] = new WeakConformance[T, T, T] {
implicit def aToC(a: T): T = a
implicit def bToC(b: T): T = b
}
implicit def IntDouble: WeakConformance[Int, Double, Double] = new WeakConformance[Int, Double, Double] {
implicit def aToC(a: Int) = a
implicit def bToC(b: Double) = b
}
implicit def DoubleInt: WeakConformance[Double, Int, Double] = new WeakConformance[Double, Int, Double] {
implicit def aToC(a: Double) = a
implicit def bToC(b: Int) = b
}
}
case class C[A <: AnyVal](val value:A) {
import WeakConformance.unify
def +[B <: AnyVal, WeakLub <: AnyVal](that:C[B])(implicit wc: WeakConformance[A, B, WeakLub], num: Numeric[WeakLub]): C[WeakLub] = {
new C[WeakLub](num.plus(wc.aToC(x), wc.bToC(y)))
}
}
and here is part of my interpreter
class Interpreter {
......
def eval(e: Expression): Any = e match {
...
case ADD(lhs, rhs) => (eval(lhs), eval(rhs)) match {
case (l: C[_], r: C[_]) => l + r // error comes here
case _ => error("...")
}
}
}
the error is like that
error: ambiguous implicit values: // shows 2 last objects declared as implicit in Numeric trait here match expected type Numeric[WeakLub]
any ideas how to make it work? I wanted to make the eval method to return C but since C[Int] is not an instance of C[Any] it doesn't solve my problem
