Re: [Haskell-cafe] "Bounds checking" pragma?
2011/11/10 Daniel Fischer :
>
> There's a problem here, unsafeAt uses an Int index into the array, while
> (!) uses the declared index type. Even skipping the bounds check, you'd
> still have to calculate the Int index for the replacement of (!).
>
>
> #ifdef OMIT_BOUNDS_CHECK
> {-# RULES
> "ArrayIndex" arr ! i = unsafeAt arr (unsafeIndex (bounds arr) i)
> #-}
> #endif
>
Thanks!
>
> (?) = unsafeAt
>
Yes, but (!) was taken as an example. There is a lot of other
functions doing bounds checking... Creating replacements for every
single function is rather tedious.
The flag pragma also has other uses. For example, we can introduce an
"overflow" flag (check every operation with Int's for overflow) ,
which may be useful for debugging. In release version this flag will
be turned off.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] "Bounds checking" pragma?
On Thursday 10 November 2011, 00:35:07, Artyom Kazak wrote:
> Hello!
>
> The (!) operator is short and nice. Unfortunately, when doing heavy
> computing, we have to use "unsafeAt" instead. It looks ugly and it is
> ugly, also.
>
> Some compilers for imperative languages like Free Pascal have an option
> to turn on/off bounds checking for arrays. Wouldn't it be nice to have
> such option in GHC? Is it possible?
>
> There is a problem: Haskell has a lot of array libraries. The only
> solution I see is a new FLAG pragma:
>
> (!) :: Array i a -> i -> a
> --definition
>
> {-# FLAG "boundsCheck" (!) = unsafeAt #-}
There's a problem here, unsafeAt uses an Int index into the array, while
(!) uses the declared index type. Even skipping the bounds check, you'd
still have to calculate the Int index for the replacement of (!).
>
> It is similar to RULES pragma, but only fires when flag is set. To set
> the flag you need to complile with option -flags="boundsCheck". Also,
> the mantainers of vector library, bytestring library, repa library and
> so on will have to include such pragmas in their code.
>
> I don't know about C++ preprocessor, though. Maybe this is already
> solvable with #define's...
#ifdef OMIT_BOUNDS_CHECK
{-# RULES
"ArrayIndex" arr ! i = unsafeAt arr (unsafeIndex (bounds arr) i)
#-}
#endif
>
> Anyway, I have to say it once again: unsafeAt is ugly and Haskell is
> beautiful. Why high-performance code should be ugly?
(?) = unsafeAt
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] "Bounds checking" pragma?
Hi, Am Donnerstag, den 10.11.2011, 01:35 +0200 schrieb Artyom Kazak: > Anyway, I have to say it once again: unsafeAt is ugly and Haskell is > beautiful. Why high-performance code should be ugly? It does not have to be ugly. Just write (!!) = unsafeAt in some common module of yours, and you have a nice fast array access. I don’t think a flag would be very helpful, because you might have some places where you want the safe access, and others where you know that it is safe to skip the check. Greetings, Joachim -- Joachim "nomeata" Breitner m...@joachim-breitner.de | nome...@debian.org | GPG: 0x4743206C xmpp: nome...@joachim-breitner.de | http://www.joachim-breitner.de/ signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] "Bounds checking" pragma?
Hello!
The (!) operator is short and nice. Unfortunately, when doing heavy
computing, we have to use "unsafeAt" instead. It looks ugly and it is
ugly, also.
Some compilers for imperative languages like Free Pascal have an option to
turn on/off bounds checking for arrays. Wouldn't it be nice to have such
option in GHC? Is it possible?
There is a problem: Haskell has a lot of array libraries. The only
solution I see is a new FLAG pragma:
(!) :: Array i a -> i -> a
--definition
{-# FLAG "boundsCheck" (!) = unsafeAt #-}
It is similar to RULES pragma, but only fires when flag is set. To set the
flag you need to complile with option -flags="boundsCheck". Also, the
mantainers of vector library, bytestring library, repa library and so on
will have to include such pragmas in their code.
I don't know about C++ preprocessor, though. Maybe this is already
solvable with #define's...
Anyway, I have to say it once again: unsafeAt is ugly and Haskell is
beautiful. Why high-performance code should be ugly?
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
