Value of the last element of a list

Question

how to get the value of the last element of a List? I\'ve noted that List.hd (or .Head) return an item, while List.tl (or .Tail) returns a List.

Is rev the List and

Answer 1

You can call List.Head to get the first element of a list, such that the below expression evaluates to true:

let lst = [1;2;3;4;5]
List.head lst = 1

However, calling List.Tail will return every element in the list after the first element, such that the below expression is true:

let lst = [1;2;3;4;5]
List.tail lst = [2;3;4;5]

Like some other people have mentioned, there isn't an efficient way in F# to get the tail end of a list, basic lists just aren't built with that functionality in mind. If you really want to get the last element you're going to have to reverse your list first, and then take the new head (which was the previous tail).

let lst = [1;2;3;4;5]
(List.head (List.rev lst) ) = 5