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From: "Ryan Bastic" <rbastic@gis.net>
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To: caml-list@inria.fr
Subject: [Caml-list] Clarification of original post [still having problems]
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Can anyone take some time and help a struggling newbie out? :-(

This stuff is still failing to parse right for my brain.

----- Original Message Follows -----
> 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)
> 

The specific problems that confuse me is that 

let rec group' ... in Array.of_list is all part of the same expression,
so how does Ocaml
let front :: group' n rest work?? firstN n input returns two arrays, and
as far as my
understanding goes, :: is a list concatenation operator. How then, does
this work?

Someone help! :)
 
> if you pop this into the toplevel, and do:
> 
> group 2 [|"Name1"; "Name2"; "Name3"; "Name4"; "Name5";|];;
> 
> you'll see the general functionality expected.
> 

-Ryan
http://malander.undrgnd.net

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