Underscore in binary literals

[Moritz Angermann]

Hi,

I for one, would like to have this in more than just BinaryLiterals (which I find rather useful as well!)
I’d like to see `_` in any numeric literal being simply ignored, as I find it makes writing and reading
numbers in source code much easier.

let i =   1_000_000 :: Int
    f =   1_123.456 :: Float
    b = 0b1100_0011

And grouping (via underscore) might be very much domain specific. (One might want to denote magnitudes
or patterns.) I ended up writing a quite a bit of stupid boilerplate[1] to support readable binary
notation[2].

Cheers,
 Moritz
—
[1]: https://github.com/angerman/data-bitcode/blob/c9818debd3dae774967c0507882b6b3bec7f0ee4/test/BitcodeSpec.hs#L22-L83
[2]: https://github.com/angerman/data-bitcode/blob/c9818debd3dae774967c0507882b6b3bec7f0ee4/test/BitcodeSpec.hs#L146-L150

> On Sep 26, 2017, at 9:19 PM, Takenobu Tani <takenobu.hs at gmail.com> wrote:
> 
> Hi Rahul,
> 
> Thanks for the explanation.
> Hmm, Is not there much need...
> 
> Thank you code example.
> I will also look at lexer for my study [1].
> 
> [1]: https://phabricator.haskell.org/D22
> 
> Thank you :) ,
> Takenobu
> 
> 
> 2017-09-26 21:58 GMT+09:00 Rahul Muttineni <rahulmutt at gmail.com>:
> Implementation-wise, it's no so difficult to include - the lexer needs to be tweaked. But it seems like a specialised use-case that will only affect a minority of users is probably not worthwhile as an extension to the language/compiler.
> 
> Maybe you can try using OverloadedStrings and implement this as a library?
> 
> ```
> newtype Binary = Binary Integer
>   deriving Num
> 
> instance IsString Binary where
>   fromString binaryLiteral = error "Code here to parse binary literal with underscores"
> 
> binaryVal :: Binary
> binaryVal = "1101_1110_0101"
> ```
> 
> Hope that helps,
> Rahul
> 
> On Tue, Sep 26, 2017 at 8:40 AM, Takenobu Tani <takenobu.hs at gmail.com> wrote:
> Dear devs,
> 
> GHC's BinaryLiterals extension is useful.
> (For example, x = 0b110111000101)
> 
> Is it difficult to include underscore(_) in the format like Verilog-HDL[1] ?
> (For example, x = 0b1101_1100_0101)
> 
> [1]: https://inst.eecs.berkeley.edu/~cs150/fa06/Labs/verilog-ieee.pdf#page=20
> 
> Regards,
> Takenobu
> 
> 
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> 
> 
> 
> 
> -- 
> Rahul Muttineni
> 
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————————————————— 
Moritz Angermann
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