Streams and call-by-need

Streams and call-by-need

[Christoph Bauer]

Hi,

do streams support call-by-need? This looks like call-by-name:

#  let s = [< '(print_endline "a"); '(print_endline "b") >]
  ;;
val s : unit Stream.t = <abstr>
# let t = [< s; s >]
  ;;
val t : unit Stream.t = <abstr>
# Stream.next t;;
a
- : unit = ()
# Stream.next t;;
b
- : unit = ()
# Stream.next t;;
a
- : unit = ()
# Stream.next t;;
b
- : unit = ()

Christoph Bauer

Re: [Caml-list] Streams and call-by-need

[Nicolas Pouillard]

On 5/26/06, Christoph Bauer <christoph.bauer@lms-gmbh.de> wrote:
> Hi,
>
> do streams support call-by-need? This looks like call-by-name:
>
> #  let s = [< '(print_endline "a"); '(print_endline "b") >]
>   ;;
> val s : unit Stream.t = <abstr>
> # let t = [< s; s >]
>   ;;
> val t : unit Stream.t = <abstr>
> # Stream.next t;;
> a
> - : unit = ()
> # Stream.next t;;
> b
> - : unit = ()
> # Stream.next t;;
> a
> - : unit = ()
> # Stream.next t;;
> b
> - : unit = ()
>

Since your stream elements make function calls they are boxed in
functions taking unit.
Thus calls are delayed, but that's not real lazy values, the function
call is always done.

-- 
Nicolas Pouillard