Add 'e' to Floating typeclass

[chessai .]

asymmetry in presence, not use.

When I was first learning Haskell, the absence of e along with the presence
of pi in Floating confused me. It is not a disservice to users to note this
asymmetry in documentation and why it is not there.

On Thu, Feb 21, 2019, 1:22 PM Carter Schonwald <carter.schonwald at gmail.com>
wrote:

> i dont see it as an assymetry, theres a lot of very simple volume / area /
> probability /geometry calculations  where pi comes up,
> i dont know any for e that aren't just exp. can you share some?
>
> On Wed, Feb 20, 2019 at 10:50 PM chessai . <chessai1996 at gmail.com> wrote:
>
>> Yeah, I think it probably shouldn't be added to the typeclass then.
>>
>> The asymmetry should probably be mentioned in the report though.
>>
>>
>> On Wed, Feb 20, 2019, 9:22 PM Carter Schonwald <
>> carter.schonwald at gmail.com> wrote:
>>
>>> either way, we're not gonna add e :)
>>>
>>> On Wed, Feb 20, 2019 at 8:30 AM Yitzchak Gale <gale at sefer.org> wrote:
>>>
>>>> Lennart's question "Is it really worth it?" is the most important one.
>>>> And no, probably it isn't.
>>>>
>>>> But Chessai is correct that this is a weird asymmetry in the Floating
>>>> class. My own experience is that I user neither e nor pi very much,
>>>> but neither one more than the other.
>>>>
>>>> Branch cuts of inverse trig functions are not relevant. The report
>>>> doesn't explicitly state this, but it's clear that these functions are
>>>> expected to return the standard ranges of values as in other
>>>> programming languages. You can be quite certain that acos (-1) is pi
>>>> in Haskell. And in fact, we have (at least on my computer)
>>>>
>>>> Prelude> acos (-1) == pi
>>>> True
>>>>
>>>> So there isn't any more or less reason to have e than pi as a separate
>>>> class member.
>>>>
>>>> On Sun, Feb 17, 2019 at 10:15 PM Lennart Augustsson
>>>> <lennart at augustsson.net> wrote:
>>>> >
>>>> > Is it really worth it?  How frequent are uses of e, except used like
>>>> exp?  On the other hand, pi has more frequent standalone use cases.
>>>> > Also, e has a simple definition (exp 1), whereas pi is somewhat more
>>>> involved.
>>>> >
>>>> > The logp1 and expm1 functions where added for good numerical
>>>> reasons.  The same would not be true for e.
>>>> >
>>>> > On Sat, Feb 16, 2019 at 21:14 chessai . <chessai1996 at gmail.com>
>>>> wrote:
>>>> >>
>>>> >> We have the 'pi' constant in the floating typeclass and some
>>>> trigonometric functions, as well as things like exp/log/expm1/log1p.
>>>> >>
>>>> >> Why not provide an 'e' constant?
>>>> >>
>>>> >> A default implementation could just be 'exp 1'.
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