[web-devel] Data.Word8 (word8 library)

Gregory Collins greg at gregorycollins.net
Fri Sep 21 09:46:41 CEST 2012

On Fri, Sep 21, 2012 at 5:11 AM, Kazu Yamamoto <kazu at iij.ad.jp> wrote:

> Hello,
> > Ignoring this, I think I can summarize:
> >
> >    - Data.ByteString.Char8 has no performance penalty: "w2c" uses
> >    "unsafeChr" which is a no-op, and GHC.Word has a RULES pragma making
> the
> >    "fromIntegral" also free (it's a narrow8Word#)
> >    - for some reason GHC is generating worse code for the Word8 versions
> of
> >    toLower than it is for the Char equivalents
> >    - consequently, there seems to be no reason to use the word8 library:
> >    not only is it not faster, it's actually a pessimization.
> My dictionary does not have the word "pessimization". Would you explain
> what do you want to say with other words?

It's a joke on "optimization" (see "optimism" vs "pessimism"), in other
words making things slower rather than faster.

Anyway, my understanding from this thread is:
> - Data.ByteString.Char8 does not have performance penalty.  So, we can
>   use the character literal (e.g. 'H') with it for code readability.
> - But the utility functions in Data.Char is slow because it handles
>   Unicode. So, we need faster utility functions specialized to Char.
> Is this correct? Should I implement the char8 library (or include
> Data.Char8 in the word8 library)?
> I know that Greg dislikes to have extra libraries but I think that
> sharing utility functions is a good thing.

Sounds correct to me. The only thing that's needed as far as I can tell is
specialized-to-ascii toUpper and toLower.

Gregory Collins <greg at gregorycollins.net>
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