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package expAbstractData
/** A base class consisting of
* - a root trait (i.e. abstract class) `Exp' with an `eval' function
* - an abstract type `exp' bounded by `Exp'
* - a concrete instance class `Num' of `Exp' for numeric literals
*/
trait Base {
type exp <: Exp
trait Exp {
def eval: Int
}
class Num(v: Int) extends Exp { self: exp =>
val value = v
def eval = value
}
}
object testBase extends App with Base {
type exp = Exp
val term = new Num(2);
Console.println(term.eval)
}
/** Data extension: An extension of `Base' with `Plus' expressions
*/
trait BasePlus extends Base {
class Plus(l: exp, r: exp) extends Exp { self: exp =>
val left = l
val right = r
def eval = left.eval + right.eval
}
}
/** Operation extension: An extension of `Base' with 'show' methods.
*/
trait Show extends Base {
type exp <: Exp1
trait Exp1 extends Exp {
def show: String
}
class Num1(v: Int) extends Num(v) with Exp1 { self: exp with Num1 =>
def show = value.toString()
}
}
/** Operation extension: An extension of `BasePlus' with 'show' methods.
*/
trait ShowPlus extends BasePlus with Show {
class Plus1(l: exp, r: exp) extends Plus(l, r) with Exp1 { self: exp with Plus1 =>
def show = left.show + " + " + right.show
}
}
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