From: "Olivier Andrieu" <oandrieu@gmail.com>
To: kirillkh <kirillkh@gmail.com>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] best and fastest way to read lines from a file?
Date: Tue, 2 Oct 2007 22:23:59 +0200 [thread overview]
Message-ID: <95513600710021323u762efd5k5ee6bdd03d7cc37@mail.gmail.com> (raw)
In-Reply-To: <e2d02be30710021102h565c7e2ax88b03a4066812816@mail.gmail.com>
On 10/2/07, kirillkh <kirillkh@gmail.com> wrote:
> OK, so I'll give up the parsing/buffering part and only leave efficient
> exception handling. This should leave the user free to do anything with it,
> but prevent performance pitfalls. The following is based on Mattias
> Engdegard's code:
>
> (* I couldn't figure out, how to declare a polymorphic exception properly *)
> exception Done of 'a
>
> let fold_file (file: in_channel)
> (read_func: in_channel->'a)
> (elem_func: 'a->'b->'b)
> (seed: 'b) =
> let rec loop prev_val =
> let input =
> try read_func file
> with End_of_file -> raise (Done prev_val)
> in
> let combined_val = elem_func input prev_val in
> loop combined_val
> in
> try loop seed with Done x -> x
>
> And the usage for line counting:
>
> let line_count filename =
> let f = open_in filename in
> let counter _ count = count + 1 in
> fold_file f readline counter 0
>
> Since it's library code, we can tolerate the little annoyance of the second
> try-catch. As far as I can tell, this code has the same performance
> characteristics as yours: no consing + tail recursion. Any other problems
> with it?
well apart from the fact that you cannot have "polymorphic exceptions"
in OCaml, this kind of code is IMHO much more natural with an
imperative loop instead of a functional one:
let fold_file read chan f init =
let acc = ref init in
begin
try while true do
let d = read chan in
acc := f d !acc
done
with End_of_file -> ()
end ;
!acc
--
Olivier
next prev parent reply other threads:[~2007-10-02 20:24 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-01 21:27 YC
2007-10-01 21:55 ` [Caml-list] " Daniel Bünzli
2007-10-01 22:29 ` YC
2007-10-01 21:55 ` Olivier Roussel
2007-10-02 12:39 ` Mattias Engdegård
2007-10-02 12:56 ` Brian Hurt
2007-10-02 16:15 ` kirillkh
2007-10-02 17:10 ` verlyck, Bruno.Verlyck
2007-10-02 18:02 ` kirillkh
2007-10-02 19:35 ` skaller
2007-10-02 21:05 ` kirillkh
2007-10-02 21:07 ` Jon Harrop
2007-10-02 20:23 ` Olivier Andrieu [this message]
2007-10-02 20:49 ` kirillkh
2007-10-02 21:10 ` Jon Harrop
2007-10-02 21:15 ` David Allsopp
2007-10-02 22:23 ` skaller
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