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

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 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@joachim-breitner.de http://www.joachim-breitner.de/

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