In Scala, how do I fold a List and return the intermediate results?

Question

I\'ve got a List of days in the month:

val days = List(31, 28, 31, ...)

I need to return a List with the cumulative sum of days:

Answer 1

Works on 2.7.7:

def stepSum (sums: List [Int], steps: List [Int]) : List [Int] = steps match { 
     case Nil => sums.reverse.tail                                                  
     case x :: xs => stepSum (sums.head + x :: sums, steps.tail) }

days
res10: List[Int] = List(31, 28, 31, 30, 31)

stepSum (List (0), days) 
res11: List[Int] = List(31, 59, 90, 120, 151)