Re: [Caml-list] Function composition in CAML

[Oleg Trott <oleg_trott@columbia.edu>]

On Sunday 08 June 2003 07:27 am, TBraibant wrote:
> Hello
>
> I have made some experimentations, but I can't find where is a bug in a
> simple piece of code
>
> I represent a polynome by a list of its coefficents
> (I know that there is a more efficient way to do this calculation (P(x) in
> fact), but it is just an expermimentation)
>
> let horner p x =
>   let v= Array.of_list p in
>   let n = Array.length v in
>   let r = ref n in
>   let f = ref (function u ->u  ) in
>     while !r <> 0 do
>       f := (function u -> !f( v.(!r)+ x*u));
>       r := !r -1 ;
>     done;
>     !f(0)
> ;;
>
> In theory, the !f(0) call shall give me P(x)...
> But it seems that the computer crash, and can't handle this line of code...
>
> Someone has an idea?
>
> Thank you

The computer does not crash, you are merely entrering an infinite loop 
because, with function composition, you couldn't keep track of the mutable 
variables in your code. A possible solution is:

let eval p x = 
  let rec aux p prod sum =
    match p with
    | [] -> sum
    | a :: b -> aux b (x*prod) (a*prod + sum)
  in aux p 1 0
;;

"eval" does not implement Horner's rule. The latter sounds like homework :)

-- 
Oleg Trott <oleg_trott@columbia.edu>

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