任意型リストのjoin(その2 by id:htid46)

join2.fsx

let join2 (elem: 'a) (lis: 'a list) =
    lis
    |> List.fold (fun a x -> match a with | [] -> [ x ] | _ -> x :: elem :: a ) []
    |> List.rev
let test1 = join2 0 [1;2;3;4;5;6] = [1;0;2;0;3;0;4;0;5;0;6] // -> true
let test2 = join2 0 [] = [] // -> true