Map that!

gistfile1.scala

  def maprec[B](f: A => B): List[B] = {

    def recur(head: A, tail: List[A]): List[B] = {
      tail match {
        case Nil => List(f.apply(head))
        case _ => f.apply(head) +: recur(tail.head, tail.tail)
      }
    }

    recur(elements.head, elements.tail)
  }

So what I remember from fpinscala is that for a tailrec version of map, you implement it using fold. You could do it all in one definition but I think to make it tailrec, the clearest way is to decompose the whole thing into separate functions.

https://gist.github.com/Jazzatola/bf4767f597c7ff7822a3

Here's a recursive implementation:

def map[A, B](as: List[A], f: A => B): List[B] = as match {
  case Nil => Nil
  case head :: tail => f(head) :: map(tail, f)
}