Re: Need hints for little exercise : write the List.concat

On 20/04/2016 16:15, Gabriel Scherer [email protected] 
[ocaml_beginners] wrote:
>
> You might find it easier to start by writing
>
> val sum : int list -> int
>
> (returning 0 on the empty list) and then "generalize" this to
>
> val concat : 'a list list -> 'a list
>

Thanks to your advice, I tried to generalize the sum function so I did this

   let rec myappend first second=
   match first with
   |[] -> second
   |hd :: tl -> hd :: (myappend tl second);;
   val myappend : 'a list -> 'a list -> 'a list = <fun>

then

   let rec myconcat alist =
   match alist with
   |[] -> []
   |hd ::tl -> myappend hd (myconcat tl);;
   val myconcat : 'a list list -> 'a list = <fun>

and I tried to do like I wanted to in my first try:

   let rec myconcat2 alist =
   match alist with
   |[] -> []
   |hd :: tl -> let rec aux first second=
                match first with
                |[] -> second
                |tete ::queue -> tete :: (aux queue second) in
                aux hd (myconcat2 tl);;
   val myconcat2 : 'a list list -> 'a list = <fun>


> There are interesting, slightly more advanced discussions to be had
> over the specific way you implemented the previous functions (some
> correct definitions are more correct than the other)
>
What do you mean?