Proposal: Add log1p and expm1 to GHC.Float.Floating

[Edward Kmett]

This does work.

MINIMAL is checked based on the definitions supplied locally in the
instance, not based on the total definitions that contribute to the
instance.

Otherwise we couldn't have the very poster-chid example of this from the
documentation for MINIMAL

class Eq a where
    (==) :: a -> a -> Bool
    (/=) :: a -> a -> Bool
    x == y = not (x /= y)
    x /= y = not (x == y)
    {-# MINIMAL (==) | (/=) #-}



On Wed, Apr 23, 2014 at 7:57 PM, John Lato <jwlato at gmail.com> wrote:

> There's one part of this alternative proposal I don't understand:
>
> On Mon, Apr 21, 2014 at 5:04 AM, Edward Kmett <ekmett at gmail.com> wrote:
>
>>
>> * If you can compile sans warnings you have nothing to fear. If you do
>> get warnings, you can know precisely what types will have degraded back to
>> the old precision at *compile* time, not runtime.
>>
>
> I don't understand the mechanism by which this happens (maybe I'm
> misunderstanding the MINIMAL pragma?).  If a module has e.g.
>
> > import DodgyFloat (DodgyFloat) -- defined in a 3rd-party package,
> doesn't implement log1p etc.
> >
> > x = log1p 1e-10 :: DodgyFloat
>
> I don't understand why this would generate a warning (i.e. I don't believe
> it will generate a warning).  So the user is in the same situation as with
> the original proposal.
>
> John L.
>
>
>> On Mon, Apr 21, 2014 at 5:24 AM, Aleksey Khudyakov <
>> alexey.skladnoy at gmail.com> wrote:
>>
>>> On 21 April 2014 09:38, John Lato <jwlato at gmail.com> wrote:
>>> > I was just wondering, why not simply numerically robust algorithms as
>>> > defaults for these functions?  No crashes, no errors, no loss of
>>> precision,
>>> > everything would just work.  They aren't particularly complicated, so
>>> the
>>> > performance should even be reasonable.
>>> >
>>> I think it's best option. log1p and exp1m come with guarantees
>>> about precision. log(1+p) default makes it impossible to depend in such
>>> guarantees. They will silenly give wrong answer
>>>
>>
>>
>
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