Re: [Caml-list] The Implicit Accumulator: a design pattern using optional arguments

[Jon Harrop <jon@ffconsultancy.com>]

On Thursday 28 June 2007 12:01:34 Thomas Fischbacher wrote:
> Jon Harrop wrote:
> > I think Thomas is referring to continuation passing style (CPS). That
> > isn't an optimization though (it slows things down) but it does let you
> > abstract away mutation. However, it is not entirely safe in the absence
> > of linear types.
>
> Which one do you prefer?
>
> let sum_nums n =
>    let rec work sum todo =
>      if todo=0 then sum
>      else work (sum+todo) (todo-1)
>    in work 0 n
> ;;
>
> let sum_nums2 n =
>    let rec work (sum,todo) =
>      if todo=0 then sum
>      else work ((sum+todo),(todo-1))
>    in work (0,n)
> ;;
>
> Certainly the first one, right?

I would write:

  let rec work sum = function
    | 0 -> sum
    | todo -> work (sum + todo) (todo - 1)

  let sum_nums n = work 0 n

because it is shorter, clearer, 65% faster and it is idiomatic ML rather than 
idiomatic Lisp.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
The OCaml Journal
http://www.ffconsultancy.com/products/ocaml_journal/?e