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).
| // naive implementation | |
| let rec length list = | |
| match list with | |
| | [] -> 0 | |
| | _::tail -> 1 + computeLength tail |
A tail recursive implementation is outlined next.
| // Tail recursive computation of List's length | |
| let length list = | |
| // Auxiliary function to compute length | |
| // It store intermediate result in acc. | |
| let rec lengthAux acc list = | |
| match list with | |
| | [] -> acc | |
| | _::tail -> lengthAux (acc+1) tail | |
| lengthAux 0 list // invoking lengthAux with acc = 0 |
Following is a more succinct implementation using List.Fold.
| let length list = | |
| List.fold | |
| (fun acc _ -> acc+1) | |
| 0 | |
| list |
Output:
> length [];; val it : int = 0 > length [1;2;3;4];; val it : int = 4 > length ['a';'b'];; val it : int = 2
