That formatted well :-(
object EnumTest extends App {
sealed trait Num { def v: Int}
case object One extends Num{ val v = 1 }
case object Two extends Num{ val v = 2 }
case object Three extends Num{ val v = 3 }
object Num {
implicit val NumEnum: scalaz.Enum[Num] = new scalaz.Enum[Num] {
override def succ(a: Num) = a match { case One => Two case Two =>
Three case Three => One}
override def pred(a: Num) = a match { case One => Three case Two =>
One case Three => Two}
override def order(x: Num, y: Num) =
scalaz.Ordering.fromInt(java.lang.Integer.compare(x.v, y.v))
override val min = Some(One)
override val max = Some(Three)
}
}
import scalaz.syntax.equal._; import scalaz.std.anyVal._
def sumVFrom(n: Num): Int = ???
assert(sumVFrom(One) === 6)
assert(sumVFrom(Two) === 5)
assert(sumVFrom(Three) === 3)
}
On Tue, Nov 8, 2016 at 10:33 AM, oxbow_lakes <[email protected]> wrote:
> Suppose I have some enumeration with a definite min and max:
>
>
>
> sealed trait Num { def v: Int}
>
> case object One extends Num { val v = 1 }
>
> case object Two extends Num { val v = 2 }
>
> case object Three extends Num { val v = 3 }
>
>
>
> I might define the enum instance as follows:
>
>
>
> object Num {
>
> implicit val NumEnum: scalaz.Enum[Num] = new scalaz.Enum[Num] {
>
> override def succ(a: Num) = a match { case One => Two case Two => Three
> case Three => One}
>
> override def pred(a: Num) = a match { case One => Three case Two => One
> case Three => Two}
>
>
> override def order(x: Num, y: Num) =
> scalaz.Ordering.fromInt(java.lang.Integer.compare(x.v, y.v))
>
>
> override val min = Some(One)
>
> override val max = Some(Three)
>
> }
>
> }
>
>
>
> I wish to perform some state transition (or fold) through the values of
> the enumeration. Let's say I wish to sum the numeric values of the above
> from some given start. How do I do this using the *succState* methods on
> Enum? The comments say that these methods are useful for looping but I'm
> struggling to figure out how.
>
>
>
> def sumVFrom(n: Num): Int = ??? //TODO: How to implement this?
>
>
> import scalaz.syntax.equal._; import scalaz.std.anyVal._
>
> assert(sumVFrom(One) === 6)
>
> assert(sumVFrom(Two) === 5)
>
> assert(sumVFrom(Three) === 3)
>
>
>
> Any help appreciated!
>
> Cheers,
> Chris
>
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