[Haskell-cafe] Bytestring map/zipWith rationale

[Nicolas Trangez]

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.

Nicolas
On Sep 12, 2013 8:11 PM, "John Lato" <jwlato at 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.schonwald at 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
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>>
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