Flattening a sealed case class hierarchy

Question

Suppose I have a sealed case class hierarchy like the following:

sealed trait Expr
case class Const(val: Double) extends Expr
case class Plus(x: Expr, y: Expr) extends Expr
case class Times(x: Expr, y: Expr) extends Expr

Is it possible to automatically convert expressions such as Plus(1,Plus(2,3)) into a HList of HLists?
Will the conversion work even inside some function f(e: Expr), i.e. when the specific structure of e is not known at compile time?

`... when the specific structure of e is not known at compile time.` Since `Expr` is a `sealed trait`, then the compiler knows all sub-classes at compile-time, e.g. exhaustiveness matching. I don't understand this comment/question - can you please explain? — Kevin Meredith, Dec 23 '15 at 19:13
I mean: from inside f, it's not explicitly known if it's been called with f(Plus(1,x)) or f(Times(a,b)) - Is that an obstacle to flattening the expression into a HList from inside f? — NietzscheanAI, Dec 23 '15 at 19:24

score 0 · Accepted Answer · edited May 23 '17 at 11:44

0

It turns out that this has already been answered on SO here and that there's a corresponding example in the Shapeless distribution as of shapeless-2.1.0-SNAPSHOT.

edited May 23 '17 at 11:44

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answered Dec 30 '15 at 18:11

NietzscheanAI

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Flattening a sealed case class hierarchy

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