[Caml-list] Clarification on some ocaml stuff

[Caml-list] Clarification on some ocaml stuff

[Ryan Bastic]

Hello all,
  A few weeks ago I posted a message asking how to create a program in
OCaml to shuffle  vector of strings into an array of arrays. Had some
problems understanding how to do it in Ocaml properly, and a kind soul
posted a very elegant solution to the problem :-) unfortunately, i still
can't understand some things from it.

  What follows is some code with comments on how it is expected to be
used, and also
where my confusion in the semantics of the code lay.

  (* Return first 'n' from input and the rest. *)
let firstN n input =
  let nInput = Array.length input in
    if n >= nInput
    then (input, [||])
    else (Array.sub input 0 n, Array.sub input n (nInput - n))

let group n input =
  let rec group' n input =
    if Array.length input = 0 then []
    else 
      let (front, rest) = firstN n input in
        (* the next line confuses me. i'm aware of :: being a list
concatenation
           operator, but in this case, shouldn't group 'n rest be
returning an array,
           because that's what firstN returns. I've experimented in the
REPL and had
           no luck in figuring it out. *)
    	front :: group' n rest
  in
    Array.of_list (group' n input)

if you pop this into the toplevel, and do:

group 2 [|"Name1"; "Name2"; "Name3"; "Name4"; "Name5";|];;

you'll see the general functionality expected.

thanks for any help,
-Ryan
http://malander.undrgnd.net

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Re: [Caml-list] Clarification on some ocaml stuff

[SooHyoung Oh]

"group' n rest" is returning 'a array list, not 'a array array.

firstN: int -> 'a array -> 'a array * 'a array
group': int -> 'a array -> 'a array list
group: int -> 'a array -> 'a array array

---
SooHyoung Oh
----- Original Message -----
From: "Ryan Bastic" <rbastic@gis.net>
To: <caml-list@inria.fr>
Sent: Friday, April 18, 2003 12:25 PM
Subject: [Caml-list] Clarification on some ocaml stuff


> Hello all,
>   A few weeks ago I posted a message asking how to create a program in
> OCaml to shuffle  vector of strings into an array of arrays. Had some
> problems understanding how to do it in Ocaml properly, and a kind soul
> posted a very elegant solution to the problem :-) unfortunately, i still
> can't understand some things from it.
>
>   What follows is some code with comments on how it is expected to be
> used, and also
> where my confusion in the semantics of the code lay.
>
>   (* Return first 'n' from input and the rest. *)
> let firstN n input =
>   let nInput = Array.length input in
>     if n >= nInput
>     then (input, [||])
>     else (Array.sub input 0 n, Array.sub input n (nInput - n))
>
> let group n input =
>   let rec group' n input =
>     if Array.length input = 0 then []
>     else
>       let (front, rest) = firstN n input in
>         (* the next line confuses me. i'm aware of :: being a list
> concatenation
>            operator, but in this case, shouldn't group 'n rest be
> returning an array,
>            because that's what firstN returns. I've experimented in the
> REPL and had
>            no luck in figuring it out. *)
>     front :: group' n rest
>   in
>     Array.of_list (group' n input)
>
> if you pop this into the toplevel, and do:
>
> group 2 [|"Name1"; "Name2"; "Name3"; "Name4"; "Name5";|];;
>
> you'll see the general functionality expected.
>
> thanks for any help,
> -Ryan
> http://malander.undrgnd.net
>
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr Archives:
http://caml.inria.fr
> Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ:
http://caml.inria.fr/FAQ/
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>

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