Question

I’m wondering how can I write a function: 'a list*int -> 'a list*list that transforms a given list to a list of lists with given maximal length.

For example: segments( [1;2;3;4;5;6;7;8;9], 2 ) => [ [1;2]; [3;4]; [5;6]; [7;8]; [9] ]

Answer 1

Here is a tail-recursive solution:

let segments xs n = 
    let rec loop n xs (count, elem) acc = 
        match xs with
        | x::xs' when count < n -> loop n xs' (count+1, x::elem) acc
        | x::xs' -> loop n xs' (1, [x]) ((List.rev elem)::acc)
        | [] -> List.rev ((List.rev elem)::acc) in
    loop n xs (0, []) []

The idea is keeping an accumulator for creating current segment and another accumulator for storing a list of segments.