AST Transformation

ast-transformation.scala

/*
 * A PROBLEM.
 *
 * EXECUTIVE SUMMARY
 *
 * I have an AST. I want to map over it with _one_ function. The function
 * should produce a valid AST i.e. the function should return an instance
 * of the same class as the one it receives.
 *
 */
object Test {

  def main(args: Array[String]): Unit = {

    trait Transformable {
      // def transform(pf: PartialFuncton[?,?]) = ???
    }

    // AST definition
    sealed trait Definition extends Transformable
    case class Class(name: String, body: List[Statement]) extends Definition

    sealed trait Statement extends Transformable
    case class VariableWrite(id: String, value: Expression) extends Statement
    case class Return(expr: Expression) extends Statement

    sealed trait Expression extends Transformable
    case class VariableAccess(id: String) extends Expression
    case class Value(value: Int) extends Expression

    // Build a simple test AST
    val ast = Class("Thingy", List(
      VariableWrite("foo", Value(42)),
      Return(VariableAccess("foo"))
    ))

    // ast transform {
    //   case x: Class => x.copy( name = x.name.reverse )
    //   case x: VariableWrite => x.copy( id = x.id.reverse )
    //   case x: VariableAccess => x.copy( id = x.id.reverse )
    //   case x: VariableAccess => VariableWrite(...) // Should NOT be allowed.
    // }
  }
}