Errata

• p. 219: The ListADT class should either define monomorphic lists:

  abstract class ListADT[A]:
     type List
     val empty: List
     def cons(x: A, list: List): List
     ...
  

  or polymorphic lists:

  abstract class ListADT:
     type List[_]
     def empty[A]: List[A]
     def cons[A](x: A, list: List[A]): List[A]
     ...
  

  The version in the book defines monomorphic lists, but refers to them as List[A] instead of List; the type argument [A] is not used and should be removed.

• p. 418: The {runner-seq} line in the Runner listing is leftover LaTeX due to last minute changes; it is not part of the code and should be ignored.