[ghc-steering-committee] Proposal: Accept proposal 37, Hex Float literals

[Simon Marlow]

No objections from me.  Looks useful and not too costly in terms of extra
complexity.

On 27 February 2017 at 21:34, Iavor Diatchki <iavor.diatchki at gmail.com>
wrote:

> Hello,
>
> I was assigned to be the shepherd for the Hex Float proposal  (
> https://github.com/ghc-proposals/ghc-proposals/pull/37), so I would like
> to propose that we accept it for implementation in GHC.
>
> This is a small change, which can be summarized as follows:
>     - allow floating point numbers to be written using hex digits.
>
> The format is exactly the same as decimal floating point numbers, except
> for:
>     - the literals start with 0x
>     - the digits are in hex
>     - the exponent symbol is `p` or `P`, instead of `e` or `E`
>     - the exponent is in base 2, rather than base 10
>
> This notation has become popular among people working with floating point
> numbers, as the numbers you write can be represented exactly, which is not
> the case for base 10 numbers.
>
> The following points were discussed:
>    - the exact format to use, compared to what's allowed by other
> languages: we decided to just follow Haskell's decimal float notation, for
> least surprise
>    - should overflow (which becomes `Inf`) result in a warning?   We
> decided that this is an orthogonal issue, also relevant to decimal floating
> point and made a GHC ticket (#13232)
>     - there is an odd interaction between floating point (both decimal and
> hex) and -XNegativeLiterals, related to negative 0, see ticket #13211
>      - changing the Read instances for Float and Double to recognize hex
> floats could break some programs, although that does not seem all that
> likely
>      - there is a question of how many extra pretty printing functions to
> add to `Numeric`: the current thinking is that maybe just one `showHFloat`
> is sufficient;  the alternative is to add 5, mirroring the
> `show[E,F,G]Float` functions for decimals.
>
> I also had a stab at implementing the basic notation here:
> https://phabricator.haskell.org/D3066
> I haven't done the changes to the libraries yet.
>
> Please let me know if you have any objections or suggestions on what might
> needs to be changed.
>
> Cheers,
> -Iavor
>
>
>
>
>
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