Re: [Caml-list] Re: Metaprogramming features

[Jon Harrop <jonathandeanharrop@googlemail.com>]

On Monday 06 October 2008 17:46:49 Chung-chieh Shan wrote:
> Jon Harrop <jonathandeanharrop@googlemail.com> wrote in article 
<200810061656.42903.jon@ffconsultancy.com> in gmane.comp.lang.caml.inria:
> > Exactly. The difference is (only) the performance characteristics.
>
> To the contrary, that is not the only difference; the timing of
> side effects (including non-termination and exceptions) can also be
> different.  We give an example at the beginning of our Section 2.

I don't follow. Your paper translates the following staged function:

  let power7 : int -> int =
    .! .<fun x -> .~(Printf.printf "power\n"; power 7 .<x>.)>.;;

into this:

  let npower7 =
    (fun () -> fun x -> (printf "power\n"; npower 7 (fun () -> x)) ()) ();;

and notes that the result is different because the former calls printf 
immediately whereas the latter defers.

Surely the discrepancy is because the translation should be:

  let npower7 =
    let e = printf "power\n"; npower 7 (fun () -> x) in
    (fun () -> fun x -> e ()) ();;

because escaped code is always evaluated before the brackets that surround it, 
so it needs to be hoisted out of the "fun () -> ..."?

-- 
Dr Jon Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?e