On Thu, Sep 12, 2013 at 12:44 PM, Nicolas Trangez <nico...@incubaid.com> wrote: > I did use that a couple of times (`xor`ing 2 ByteStrings together), and was > surprised by the omission back then, but IIRC (can't validate now), there's > a specialised zipWith (as proposed) in the module (with some other name, > obviously), which is not exported, but used when you 'pack' the result of > 'zipWith' when the result is '[Word8]'... You might want to look into that.
This is correct - there is a RULES pragma that rewrites `pack (zipWith f)` into a more efficient `zipWith'` function of the type desired (see the bytestring package). I was very concerned about this when writing lots of bytestring xor code for crypto-api and was pleased to find that, if the syntactic form matches, things get optimized as you desire. Thomas > > Nicolas > > On Sep 12, 2013 8:11 PM, "John Lato" <jwl...@gmail.com> wrote: >> >> Carter: we don't have both. We have one function from each category. My >> guess is nobody's ever really needed a really fast zipWith :: >> (Word8->Word8->Word8) -> ByteString -> ByteString -> ByteString; that's the >> only reason I can think of for its omission. >> >> >> On Thu, Sep 12, 2013 at 10:45 AM, Carter Schonwald >> <carter.schonw...@gmail.com> wrote: >>> >>> Scott: benchmark the two and you'll see why we have both :-) >>> >>> >>> On Thursday, September 12, 2013, Scott Lawrence wrote: >>>> >>>> On Thu, 12 Sep 2013, Tom Ellis wrote: >>>> >>>>> On Thu, Sep 12, 2013 at 09:21:20AM -0400, Scott Lawrence wrote: >>>>>> >>>>>> Something's always bothered me about map and zipWith for ByteString. >>>>>> Why is it >>>>>> >>>>>> map :: (Word8 -> Word8) -> ByteString -> ByteString >>>>>> >>>>>> but >>>>>> >>>>>> zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> >>>>>> [a] >>>>> >>>>> >>>>> Well, what if you wanted to zipWith a function of type "Word8 -> Word8 >>>>> -> >>>>> Foo" instead of "Word8 -> Word8 -> Word8"? >>>> >>>> >>>> Then I would do what I do with map, and call `unpack` first. >>>> >>>> Either of the two options is usable: >>>> >>>> map :: (Word8 -> Word8) -> ByteString -> ByteString >>>> zipWith :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString -> >>>> ByteString >>>> (or) >>>> map :: (Word8 -> a) -> ByteString -> [a] >>>> zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a] >>>> >>>> I just don't understand why we have one from each. >>>> >>>> -- >>>> Scott Lawrence >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskell-Cafe@haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe@haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
