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Today's Topics:
1. Re: Compiling C into Haskell (Chadda? Fouch?)
2. Re: Compiling C into Haskell (Heinrich Apfelmus)
3. Re: Compiling C into Haskell (Hein Hundal)
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Message: 1
Date: Wed, 14 Apr 2010 12:20:14 +0200
From: Chadda? Fouch? <[email protected]>
Subject: Re: [Haskell-beginners] Compiling C into Haskell
To: Hein Hundal <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=UTF-8
On Tue, Apr 13, 2010 at 2:39 PM, Hein Hundal <[email protected]> wrote:
> Thanks Allan!
>
>    I was hoping the C-Haskell mix would work. I am glad to hear that you
> have good things to say about it.
>
> Â Â Â My main reason for thinking about the C-to-Haskell compiler was to
> address the question "Say you had a C program. Can you always convert it to
> Haskell in such a way that the compiled Haskell is not too slow and does not
> need too much memory?"Â Supposing that too slow means slower than 1/4 the
> speed of C and too much memory means twice the memory of C.
>
> Â Â Â Do you know the answer to this question?
I would say probably yes, since Haskell can do much of the same thing
C does or simulate it closely... But that's not idiomatic Haskell and
thus very uninteresting and probably unreadable. A C to idiomatic
Haskell compiler would be more interesting but extremely hard to write
and the results would probably be pretty slow (since a good and fast
translation would necessarily imply some change of algorithms and
data-structure and so be too hard even for a smart compiler (needs a
full AI ! ;)).
If the question is : Can we always write a fast Haskell equivalent ?
The response is probably yes (when we can write an Haskell equivalent)
but with some effort and not mechanically.
Of course, when we have a good enough C library, it may be better to
just use the FFI in practice.
--
Jedaï
------------------------------
Message: 2
Date: Wed, 14 Apr 2010 12:21:45 +0200
From: Heinrich Apfelmus <[email protected]>
Subject: [Haskell-beginners] Re: Compiling C into Haskell
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8
Brent Yorgey wrote:
> Hein Hundal wrote:
>>
>> I was hoping the C-Haskell mix would work. I am glad to hear that
>> you have good things to say about it.
>>
>> My main reason for thinking about the C-to-Haskell compiler was to
>> address the question "Say you had a C program. Can you always
>> convert it to Haskell in such a way that the compiled Haskell is
>> not too slow and does not need too much memory?" Supposing that
>> too slow means slower than 1/4 the speed of C and too much memory
>> means twice the memory of C.
>>
>> Do you know the answer to this question?
>
> My guess is that the answer is technically "no". If I recall
> correctly, there are some imperative data structures where the best
> known time complexity for a functional version is worse than the
> imperative version by a factor of (log n), so in that case you
> wouldn't be able to stay within a constant factor of C.
Well, you can always fall back to arrays in the ST monad...
> However, I think in practice the answer is usually "yes"; but it
> might be hard to do it via a mechanical compilation. Idiomatic (and
> fast) Haskell is often organized very differently than corresponding
> C code.
If you already have a C program, then it's probably easiest to link it
in with the Foreign Function Interface.
Regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
------------------------------
Message: 3
Date: Wed, 14 Apr 2010 04:34:32 -0700 (PDT)
From: Hein Hundal <[email protected]>
Subject: Re: [Haskell-beginners] Compiling C into Haskell
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Thank you to everyone who responded.
My main question was "Say you had a C program. Can you always
convert it to Haskell in such a way that the compiled Haskell
is not too slow and does not need too much memory?" supposing
that too slow means slower than 1/4 the speed of C and too much
memory means twice the memory of C.
Let me summarize some of your responses:
1) The general consensus seems to be the answer is probably yes.
The exceptions, if there are any, are C programs with complex
data structures.
2) One of the simpler ways to get the speed and memory
efficiency of C is using the ST monad.
3) The "Foreign Function Interface" (FFI) is sometimes used by
Haskell programmers to improve the speed or memory efficiency
of a slow or memory intensive subroutine.
4) For my particular project, I should look into "hmatrix"
which binds to LAPACK, a linear algebra package that I have
used before.
5) The conversion process from the C program to the speedy
Haskell program is probably not simple.
These responses were great!
Cheers,
Hein
------------------------------
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