///|
pub(all) struct ClassificationPruningStep {
  alpha : Double
  model : ClassificationTree
  node_count : Int
  leaf_count : Int
} derive(Eq, Debug)

///|
pub(all) struct RegressionPruningStep {
  alpha : Double
  model : RegressionTree
  node_count : Int
  leaf_count : Int
} derive(Eq, Debug)