"ocaml_beginners"::[] Re: Generate the combinations of K distinct objects chosen from an N-element l

This is probably a question of personal taste, but I would
not use l as a variable name when I optimize for
readability. If performance is not critical I'd just make a
list with all of them.

let cons h t = h :: t;;
let rec comb n k = 
  match (n, k) with
    (0, 0) -> [[]]
  | (0, _) -> []
  | (_, _) -> 
      List.rev_append 
        (List.map (cons (n-1)) (comb (n-1) (k-1)))
        (comb (n-1) k);;


----- Original Message ----
From: roparzhhemon <roparzhhemonyahoo.com.br>
To: ocaml_beginners@yahoogroups.com
Sent: Sunday, November 12, 2006 1:03:44 PM
Subject: "ocaml_beginners"::[] Re: Generate the
combinations of K distinct objects chosen from an N-element
list

--- In ocaml_beginners@yahoogroups.com, "Ulrich"
<ulrivo...> wrote:
> 
> But this is not so beauty and readable as the Prolog
solution:

   Well, maybe you think that because you're new to ocaml.
Your
"next_vect" function looks quite readable and
short to me.

  here's how I would do it (without having to define a new
type) :

  let rec combinations k l=
   if k=0 then [[]] else
   if List.length(l)<k then [] else 
  let head=List.hd(l) and tail=List.tl(l) in
  let first_part_of_answer=List.map(function
y->head::y)(combinations (k-1) tail)
 and second_part_of_answer=combinations(k)(tail) in
 first_part_of_answersecond_part_of_answer

 This code optimizes readibility, not performance.  

     Hope this helps ...

                                                            
      Ewan





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The archives of the very official ocaml list (the seniors'
one) can be found at http://caml.inria.fr
Attachments are banned and you're asked to be polite, avoid
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