The code snippets listed below defines a function to compute the length of a give list using F#. Note that these functions are also called polymorphic function, as they work with any type of list (as shown in the output).

A tail recursive implementation is outlined next.

Following is a more succinct implementation using List.Fold.

Output:

> length [];;
val it : int = 0
> length [1;2;3;4];;
val it : int = 4
> length ['a';'b'];;
val it : int = 2