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From: ijtrotts@ucdavis.edu
To: caml-list@inria.fr
Subject: Re: [Caml-list] Python's yield, Lisp's call-cc or C's setjmp/longjmp in OCaml
Date: Tue, 16 Dec 2003 22:30:23 -0800
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On Tuesday 16 December 2003 10:10, Dustin Sallings wrote:
> On Dec 16, 2003, at 10:42, Brian Hurt wrote:
> > By my measurements, Ocaml's exceptions are faster than C's
> > setjmp/longjmp.
> > Ocaml doesn't provide first-class continuations, but most of the things
> > people actually do with call-cc can be done in other ways in Ocaml.  I
> > don't know what Python's yield instruction does.
>
> Simple example:
>
> from __future__ import generators
>
> def number(max):
>      for i in range(max):
>          if(i % 2 == 0):
>              yield i, "Even"
>          else:
>              yield i, "Odd"
>
> for n in number(10):
>      print n
>
> 	The output of this example is as follows:
>
> (0, 'Even')
> (1, 'Odd')
> (2, 'Even')
> (3, 'Odd')
> (4, 'Even')
> (5, 'Odd')
> (6, 'Even')
> (7, 'Odd')
> (8, 'Even')
> (9, 'Odd')
>
> 	It's basically a special case of an upward continuation (or is it
> downward? I'm bad with terminology).  I think you can get pretty close
> to this behavior with streams, but it's still not as easy as a return
> statement that has a resume type thing.
  
Why not do this:

# let rec number() =
   let i=ref(-1) in fun() ->
    incr i; 
    !i, if !i mod 2 = 0 then "Even" else "Odd";;
val number : unit -> unit -> int * string = <fun>
# let n=number();;
val n : unit -> int * string = <fun>
# Array.init 10 (fun _ -> n());;
- : (int * string) array =
[|(0, "Even"); (1, "Odd"); (2, "Even"); (3, "Odd"); (4, "Even"); (5, "Odd");
  (6, "Even"); (7, "Odd"); (8, "Even"); (9, "Odd")|]

?

Issac


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