Re: [Caml-list] Immutable strings

[Gerd Stolpmann <info@gerd-stolpmann.de>]

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Am Freitag, den 04.07.2014, 17:01 -0400 schrieb Markus Mottl:
> I agree that the new concept has some noteworthy downsides as
> demonstrated in the Lexing-example.  Your proposed solution 2
> (stringlike) would probably solve these issues from a safety point of
> view.  The downside is that the complexity of string-handling would
> increase even more, because then we would have three types to deal
> with.  I personally prefer safety over convenience, but other people's
> (especially beginner's) mileage may vary.

Well, the complexity can be reduced a bit by using phantom types:

type string = [`String] stringlike
type bytes = [`Bytes] stringlike

and then just define function-by-function what is permitted:

val get : 'a stringlike -> int -> char
val set : [`Bytes] stringlike -> int -> char -> unit
val sub : 'a stringlike -> int -> int -> [`String] stringlike
val sub_bytes : 'a stringlike -> int -> int -> [`Bytes] stringlike

etc., and the modules String and Bytes would just contain aliases of
these functions with monomorphed typing.

I don't know, though, whether we can be safe to never see the
polymorphic typing when just using string and bytes. It would be a bit
surprising for beginners to see that, and you sometimes would have to
deal with unresolved type variables.

> The Bigarray-approach doesn't seem appealing to me.  Strings are much
> more lightweight, since they can be allocated cheaply on the
> OCaml-heap.  E.g. String.create is about 10x-100x faster than
> Bigarray.create.  That seems too big to ignore.

Oh, we ignore already that Unix.read and Unix.write copy all data
through an additional buffer because we cannot pass an OCaml string
directly to the OS while another thread could relocate this string. So
that copy would be eliminated. So I'd guess you are normally even faster
with bigarrays, at least when you only look at the use as I/O buffers.
But there might be other uses where this is different.

Gerd



> 
> Regards,
> Markus
> 
> On Fri, Jul 4, 2014 at 3:18 PM, Gerd Stolpmann <info@gerd-stolpmann.de> wrote:
> > Hi list,
> >
> > I've just posted a blog article where I criticize the new concept of
> > immutable strings that will be available in OCaml 4.02 (as option):
> >
> > http://blog.camlcity.org/blog/bytes1.html
> >
> > In short my point is that it the new concept is not far reaching enough,
> > and will even have negative impact on the code quality when it is not
> > improved. I also present three ideas how to improve it.
> >
> > Gerd
> > --
> > ------------------------------------------------------------
> > Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
> > My OCaml site:          http://www.camlcity.org
> > Contact details:        http://www.camlcity.org/contact.html
> > Company homepage:       http://www.gerd-stolpmann.de
> > ------------------------------------------------------------
> >
> >
> >
> > --
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> 
> 
> 
> -- 
> Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com
> 

-- 
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Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
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