Question

I have this function that uses foldright to append the two lists

def append[T](l1: List[T], l2: List[T]): List[T] = (l1 :\ l2) ((a,b) => a::b)

The scala returns:

val l1 = List(1,2,3,4,5)
val l2 = List(6,7,8,9,10)
println(append(l1,l2))
Result: List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

As starting from right to left, the result should not return opposite? Why returns in this way?

Answer 1

foldRight is execute from right to left, so the iteration is,

1: a is 5, b is 6, 7, 8, 9, 10, result is 5, 6, 7, 8, 9, 10

2: a is 4, b is 5, 6, 7, 8, 9, 10, result is 4, 5, 6, 7, 8, 9, 10

…

final result is 1, 2, 3, …, 8, 9, 10