[Haskell-cafe] Re: Re: instance Eq (a -> b)

[Ashley Yakeley]

Why is a function that gets a bunch of strict ByteStrings out of a lazy
one exposed?

In any case, it sounds like a similar situation to (==) on Float and
Double. There's a mismatch between the "Haskellish" desire for a law on
(==), and the "convenient" desire for -0.0 == 0.0, or for exposing
toChunks. Which one you prefer depends on your attitude. My point is not
so much to advocate for the Haskellish viewpoint than to recognise the
tension in the design. Float and Double are pretty ugly anyway from a
Haskell point of view, since they break a bunch of other desirable
properties for (+), (-) and so on.

The theoretical reason for using floating point rather than fixed point
is when one needs relative precision over a range of scales: for other
needs one should use fixed point or rationals. I added a Fixed type to
base, but it doesn't implement the functions in the Floating class and I
doubt it's as fast as Double for common arithmetic functions.

It would be possible to represent the IEEE types in a Haskellish way,
properly revealing all their ugliness. This would be gratifying for us
purists, but would annoy those just trying to get some numeric
calculations done.

-- 
Ashley Yakeley


On Mon, 2010-04-19 at 15:32 -0400, Edward Kmett wrote:

> Because it is the most utilitarian way to get a bunch of strict
> ByteStrings out of a lazy one.
> 
> Yes it exposes an implementation detail, but the alternatives involve
> an unnatural amount of copying.
> 
> -Edward Kmett
> 
> 
> On Sat, Apr 17, 2010 at 6:37 PM, Ashley Yakeley <ashley at semantic.org>
> wrote:
> 
>         Ketil Malde wrote:
>         
>                 Do we also want to modify equality for lazy
>                 bytestrings, where equality
>                 is currently independent of chunk segmentation?  (I.e.
>                 
>                  toChunks s1 == toChunks s2 ==> s1 == s2  
>                 but not vice versa.)
>         
>         
>         
>         
>         Why is toChunks exposed?
>         
>         -- 
>         Ashley Yakeley
>         
>         
>         
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> 
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