HELP! dependent type in Scala to decide return type of function!

[Rutvik Patel]

I am working on implementation of simple imperative language. I am trying to follow pure functional code only in order to apply in practice what I have learned recently. 

here is my ADT

sealed trait Syntax
case class Num(value: Long) extends Syntax
case class Add[A, B](left: A, right: B) extends Syntax

here is my type class

trait Construct[A] {
  type S <: Syntax
  def reduce(a: A): S
}

here is my type class instance for Add

implicit def addConstruct[A, B](implicit lc: Construct[A], rc: Construct[B]) = new Construct[Add[A, B]] {
    override type S <: ???
    override def reduce(a: Add[A, B]): S = a match {
      case Something1 => Add(lc.reduce(left), right)                // returning Add
      case Something2 => Add(left, rc.reduce(right))               // returning Add
      case Something3 => Num(x + y)                                     // returning Num
   }
}

what can I do to make my reduce function to return Num OR Add?

Is there anyway that I can manage it using Shapeless or some other workaround?

I need help and just pointing out on right direction would be enough!

Thanks!

[Miles Sabin]

Hi Rutvik,

This mailing list is deprecated in favour of shapeless's gitter
channel: I recommend you take your question there ... there will be a
lot of in the channel who will be able to help you with it,

https://gitter.im/milessabin/shapeless

Yours,


Miles

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[Rutvik Patel]

Thank you Miles! 

Rutvik.

> email to shapeless-dev+unsubscribe@googlegroups.com.

> For more options, visit https://groups.google.com/d/optout.

--
Miles Sabin
tel: +44 7813 944 528
skype: milessabin
gtalk: mi...@milessabin.com
http://milessabin.com/blog
http://twitter.com/milessabin

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