[ghc-steering-committee] #477: Unicode ellipsis, recommendation: accept

[Vladislav Zavialov (int-index)]

My -1 is firm. After some digging, I found out that the two dots are the intended notation, not just a shorthand for three dots. If you look at "Ronald L. Graham, Donald E. Knuth, and Oren Patashnik. Concrete Mathematics. Addison–Wesley, second edition, 1994”, you will find the following passage:

    For our next problem let's consider a handy new notation, suggested by C. A. R. Hoare and Lyle Ramshaw, for intervals of the real line: [α .. β] denotes the set of real numbers x such that α ≤ x ≤ β. This set is called a closed interval because it contains both endpoints α and β. The interval containing neither endpoint, denoted by (α .. β), consists of all x such that α < x < β; this is called an open interval.

The book is typeset beautifully, and I believe they could’ve used three dots if they wanted, but they used two. Since then, the Hoare-Ramshaw interval notation has been incorporated into various programming languages, including Pascal and Haskell.

I have no idea why the proposal uses three dots, actually.

- Vlad

> On 1 Mar 2022, at 17:42, Joachim Breitner <mail at joachim-breitner.de> wrote:
> 
> Hi,
> 
> it’s a worthwhile observation that we (somewhat oddly) use a two-dot
> ellipsis in ASCII-Haskell, and Artem took this up on Github to ponder
> if we should allow ASCII ... as well, but I am not convinced. I wrote
> on the Github thread:
> 
>> Hmm, I am not sure I agree that it's confusing. At least to me, from
>> the start when I saw Haskell, the ascii .. meant what's \ldots in
>> LaTeX, and what I tend to write as three close-to-each other dots on
>> paper and is semantically an ellipsis, which in Unicode has a
>> codepoint with that names that in most fonts looks like what you
>> expect it to…
>> 
>> So the .. is an ASCII cludge like all others (probably because ... is
>> unnecessarily wide).
>> 
>> The analogue is \ for λ - just because the left leg is missing we
>> wouldn't use a unrelated look-alike like \ for the unicode variant,
>> nor ask to be able to write ,\ in ASCII for a better approximation of
>> the real letter.
>> 
>> TL;DR: no need to change ASCII-Haskell, and let's use the
>> semantically correct ellipsis symbol in Unicode-Haskell.
> 
> Vlad, how firm is your -1? If you feel strongly enough about it (which
> is of course absolutely fine), I’d maybe just put this up for a vote?
> It’s a mostly aesthetical, superficial change where voting may be more
> efficient than long discussions.
> 
> Cheers,
> Joachim
> 
> -- 
> Joachim Breitner
>  mail at joachim-breitner.de
>  http://www.joachim-breitner.de/
> 
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