How to fix list tail with match recursion? [Scala]

Question

This function is taking list and one of two functions below and have to match every element in list.

val sqrt = (x: Double) => x * x val doubleValue = (x: Double) => 2 * x val yoman = (list: List[Double], func: Function[Double, Double]) => list match { case head :: tail => func(head) :: yoman(tail, func) case Nil => list } yoman(List(3.0, 4.0, 99.0), sqrt) yoman(List(-5.0, 1.0, 9.0), doubleValue)

Now I have a problem with first case:

Error:(5, 39) recursive lazy value yoman needs type case head :: tail => func(head) :: yoman(tail, func) ^

Why is yoman a val containing a lambda instead of a def? — Clashsoft
– Clashsoft, Commented Oct 21, 2018 at 13:50

pedrorijo91 · Accepted Answer · 2018-10-21 13:40:46Z

for recursive functions you need to specify the return type

 val yoman: (List[Double], Function[Double, Double]) => List[Double] = (list: List[Double], func: Function[Double, Double]) => list match { case head :: tail => func(head) :: yoman(tail, func) case Nil => list }

as you can see, you declare yoman, followed by the type (function that received a list and another function, and returns a list double), and then the body itself

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