[Caml-list] Thanks: C style for loop

["Jeff Henrikson" <jehenrik@yahoo.com>]

Awesome, thanks.  What an impressive tool.  I've gotta learn it for myself so I can do all the things I was never able to do with
the C preprocessor!


Jeff Henrikson

> -----Original Message-----
> From: owner-caml-list@pauillac.inria.fr
> [mailto:owner-caml-list@pauillac.inria.fr]On Behalf Of Daniel de
> Rauglaudre
> Sent: Thursday, October 11, 2001 4:59 AM
> To: caml-list@inria.fr; jprevost@panasas.com
> Subject: Re: [Caml-list] C style for loop
>
>
> Hi,
>
> On Thu, Oct 11, 2001 at 01:47:07AM -0400, Jeff Henrikson wrote:
>
> > Okay, so maybe I should be more specific about what I want in a
> > "C-style for loop."  Its readablity merits are hopefully self
> > evident.  Well, unless you're a compulsive CPS addict who wishes
> > even his grocery list could be written to tail recurse. . .
>
> > (*  loop var | init val | while | expr for next val *)
> > for     c         0      (c<10)        (c+1)         do
> >   (* bla *)
> > done;
>
> ------------------------------------- file cloop.ml
> #load "q_MLast.cmo";
> #load "pa_extend.cmo";
>
> open Pcaml;
>
> value gensym =
>   let cnt = ref 0 in
>   fun var ->
>     let x = do { incr cnt; cnt.val } in
>     var ^ "_gensym" ^ string_of_int x
> ;
>
> value gen_for loc v iv wh nx e =
>   let loop_fun = gensym "iter" in
>   <:expr<
>     let rec $lid:loop_fun$ $lid:v$ =
>       if $wh$ then do { $e$; $lid:loop_fun$ $nx$ } else ()
>     in
>     $lid:loop_fun$ $iv$ >>
> ;
>
> EXTEND
>   expr: LEVEL "expr1"
>     [ [ "for"; v = LIDENT; iv = expr LEVEL "simple"; wh = expr LEVEL "simple";
>         nx = expr LEVEL "simple"; "do"; e = expr; "done" ->
>           gen_for loc v iv wh nx e ] ]
>   ;
> END;
> -------------------------------------
>
> Compilation:
>    $ ocamlc -pp camlp4r -I `camlp4 -where` -c cloop.ml
>
> Example under the toplevel:
>    $ ocaml -I `camlp4 -where`
> 	   Objective Caml version 3.02+7 (2001-09-29)
>
>    # #load "camlp4o.cma";;
> 	   Camlp4 Parsing version 3.02+7 (2001-09-29)
>
>    # #load "cloop.cmo";;
>    # for i = 0 to 10 do print_int i; done;; (* normal loop *)
>    012345678910- : unit = ()
>    # for c 0 (c<10) (c+1) do print_int c; done;;
>    0123456789- : unit = ()
>    # for c 0 (c<10) (c+3) do print_int c; done;;
>    0369- : unit = ()
>
> Compilation:
>    $ cat foo.ml
>    for c 0 (c<10) (c+2) do print_int c; done
>    $ ocamlc -pp "camlp4o ./cloop.cmo" -c foo.ml
>    $
>
> Pretty print the resulting program:
>    $ camlp4o ./cloop.cmo pr_o.cmo foo.ml
>    let rec iter_gensym1 c =
>      if c < 10 then begin print_int c; iter_gensym1 (c + 2) end
>    in
>    iter_gensym1 0;;
>
> Hope this help.
>
> --
> Daniel de RAUGLAUDRE
> daniel.de_rauglaudre@inria.fr
> http://cristal.inria.fr/~ddr/
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