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[Caml-list] Why is (@) written in O'Caml?
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Date: -- (:)
From: Pal-Kristian Engstad <engstad@n...>
Subject: Re: [Caml-list] Why is (@) written in O'Caml?
On Thursday 05 December 2002 12:47 pm, Oleg wrote:
> let rec (@) l1 l2 =
>   match l1 with
>     [] -> l2
>
>   | hd :: tl -> hd :: (tl @ l2)
>
> The O'Caml implementation of (@) is recursive and not tail-recursive. All
> one really has to do during "append" is copy l1 and set the last element's
> CDR to l2. I can see why this can not be done in O'Caml itself, but since
> (@) is such a common operation, I'm wondering why it was decided to
> implement it inefficently in O'Caml itself?

You say you want to copy l1 and then set the last element of tail to l2? But, 
that is _exactly_ what the function above does! 

let copy l1 = 
  match l1 with
    [] -> []
  | hd :: tl -> hd :: copy tl

Right? So, the only change is the extra argument l2, that is being appended 
onto the list when l1 is empty. 

PKE.
-- 
  _       
  \`.       Pål-Kristian Engstad, Senior Software Engineer,
   \ `|     Naughty Dog, Inc., 1315 3rd Street Promenade, 
  __\ |`.   Santa Monica, CA 90046, USA. (310) 752-1000 x799. 
    /  /o   mailto:engstad@naughtydog.com http://www.naughtydog.com
   /  '~    mailto:mrengstad@yahoo.com    http://www.engstad.com
  / ,'      Hang-gliding Rulez!
  ~'

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