Re: [Sml-list] [Smlnj-list] Loops

[Brian P. O'H. <br...@cm...>]

> I was wondering if SML can envoke an iterative loop ( i.e while (...) do ...
> od )

Indeed it does.  The syntax is
while (expr) do (expr).
For example, suppose that I desire to count from 1 to 10.  Then I could do:

let val n = ref 1 in
while (!n <= 10) do
  let val () = TextIO.print ((Int.toString (!n)) ^ "\n") in
    n := !n + 1
  end
end

>
> or are all loops strictly recursive ( gnu ).

There is, of course, nothing wrong with recursion; I have never
actually used while in my sml code.  I could the same thing this way:

(* Generate a list of the integers from m to n *)
val intsFromTo = fn (m, n) =>
  let val rec intsFromTo' = fn a => fn c =>
    if (c < m) then
      a
    else
      intsFromTo' (c :: a) (c - 1)
  in
    intsFromTo' [] n
  end

(* Now print the numbers from 1 to 10 *)
val () = List.app (fn n=> TextIO.print ((Int.toString n) ^ "\n"))
(intsFromTo (1, 10))

Note that these functions should both be made iterative by the
compiler, as they are tail recursive.  I prefer to do things like this
the recursive and applicative way because it is more adaptable and
cleaner (no refs), though one might argue that while is more
understandable.  I hope that that helps.
-Brian