# Why is Greek ano teleia a valid identifier character?

**URL:** <https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442>\
**Category:** Internals & Design\
**Tags:** syntax\
**Created:** [July 17, 2018, 6:07pm UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442 "2018-07-17T18:07:42Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![mlhetland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mlhetland/32/283_2.png) [@mlhetland](https://discourse.julialang.org/u/mlhetland)\
**Post date:** [July 17, 2018, 6:07pm UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/1 "2018-07-17T18:07:42Z")

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It seems Greek ano teleia (U+0387) is one of the “Punctuation, other” characters (along with primes) permitted as part of identifiers. What is the rationale, here? Semantically, it doesn’t seem to make sense, and it looks a bit confusing – as it’s (at least in many fonts) very similar to the dot operator (U+22c5), i.e., `\cdot`. Also, it’s essentially the same as – i.e., normalizes to – the middle dot (U+00b7), which is _not_ permitted. Actually, it is even normalized to the middle dot when parsed as a symbol, even though the symbol cannot be written directly using this character!

```julia
julia> x·y = 42 # Using U+0387
42

julia> x⋅y = 42 # Using U+22c5
⋅ (generic function with 1 method)

julia> x·y = 42 # Using U+00b7
ERROR: syntax: invalid character "·"

julia> name = "x·y"

julia> name[2]
'·': Unicode U+0387 (category Po: Punctuation, other)

julia> String(Meta.parse(name))[2]
'·': Unicode U+00b7 (category Po: Punctuation, other)

```

… and just to underscore the point:

```julia
julia> Meta.parse(String(Meta.parse(name)))
ERROR: Base.Meta.ParseError("invalid character \"·\"")

```

Given that it seems to have been singled out for inclusion (at least in the pure-Julia rewrite of the parser, `JuliaParser.jl`, it’s listed along, alongside the three primes), I guess there may be a reason for including it, but … it seems it might be just as sensible to disallow it, just like, say, the (canonical) middle dot character is?

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**Author:** ![mlhetland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mlhetland/32/283_2.png) [@mlhetland](https://discourse.julialang.org/u/mlhetland)\
**Post date:** [July 17, 2018, 6:17pm UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/2 "2018-07-17T18:17:44Z")

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While we’re at it, I wouldn’t mind permitting the middle dot (and the ano teleia, for that matter), normalizing it (or them) to the dot operator. On a Mac, you get the middle dot (at least on my Norwegian keyboard) by pressing alt-shift-`.`, which is easier than using `\cdot`-tab (and it’s what I usually use to indicate the dot operator outside Julia or \mathrm{\TeX}).

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**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [July 17, 2018, 7:41pm UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/3 "2018-07-17T19:41:36Z")

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> [@mlhetland](#):
>
> It seems Greek ano teleia (U+0387) is one of the “Punctuation, other” characters (along with primes) permitted as part of identifiers. What is the rationale, here?

That codepoint has the property `Other_ID_Continue`, and [UAX#31](http://unicode.org/reports/tr31/) recommends that it be allowed in programming-language identifiers (mainly for backward compatibility, it says). e.g. `x·y` is also a valid identifier in Python 3 for the same reason.

Julia allows identifiers in a large superset of UAX#31, but I think it makes sense to continue to accept UAX#31 identifiers as a subset where possible, if only to ease interoperability with other languages.

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**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [July 17, 2018, 7:48pm UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/4 "2018-07-17T19:48:07Z")

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> [@mlhetland](#):
>
> While we’re at it, I wouldn’t mind permitting the middle dot (and the ano teleia, for that matter), normalizing it (or them) to the dot operator.

> <https://github.com/JuliaLang/julia/pull/25157>
>
> It includes an enhancement discussed in #25098 
> 
> (See also https://discourse.j…ulialang.org/t/inconsistencies-in-some-methods-and-more/7788)

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<div class="post-metadata">

**Author:** ![mlhetland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mlhetland/32/283_2.png) [@mlhetland](https://discourse.julialang.org/u/mlhetland)\
**Post date:** [July 18, 2018, 11:09am UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/5 "2018-07-18T11:09:30Z")

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Ah, I see.

Yes, indeed, following UAX#31 does seem to make sense – though I guess that would mean that this decision depends on the Unicode version in use? (It says “The exact list of characters covered by the Other\_ID\_Start and Other\_ID\_Continue properties depends on the version of Unicode.”)

Either way, the examples given in UAX#31 are:

> U+1369 ETHIOPIC DIGIT ONE…U+1371 ETHIOPIC DIGIT NINE  
> U+00B7 ( · ) MIDDLE DOT  
> U+0387 ( · ) GREEK ANO TELEIA  
> U+19DA ( ᧚ ) NEW TAI LUE THAM DIGIT ONE

Rather than using the `Other_ID_Continue` property, these (seemingly arbitrary) examples are explicitly listed as the ones accepted in `JuliaParser.jl`. Or do these in fact cover all the cases (despite the phrasing “… includes characters such as the following”)?

Anyway: One issue here is that we _don’t_ cover the ones listed – notably U+00b7 (which is part of the issue in my example, above). I came across [the pull request you](https://github.com/JuliaLang/julia/pull/25157) referenced earlier, but didn’t at the time realize that `\cdotp` was, in fact, U+00b7. So … making `\cdot` equal to `\cdotp` would seem to muddle things even further, then, since we’re currently normalizing the ano teleia into `\cdotp` (which, according to the UAX#31, _should_ be permitted in identifiers, but currently isn’t).

So despite my initially preferring to make `\cdotp` equal to `\cdot`, I guess this would be an argument _against_ that, and for rather making `\cdotp` an identifier characer, in accordance with UAX#31. I’m not sure I like it, but it does seem more consistent – unless we either ban the ano teleia _or_ stop normalizing it to `\cdotp` in names.

Or…?

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**Author:** ![Iagoba\_Apellaniz](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/iagoba_apellaniz/32/34406_2.png) [@Iagoba\_Apellaniz](https://discourse.julialang.org/u/Iagoba_Apellaniz)\
**Post date:** [July 18, 2018, 11:28am UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/6 "2018-07-18T11:28:48Z")

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In the spanish keyboard layout U+00B7 is typed with SHIFT + 3. I think it is very convenient to identify U+00B7 with some common operator, say `\cdot[TAB]`.

Is U+0387 so accessible by the Greek layout? Indeed if it is, I would map it to `\cdot[TAB]` too. At least if there is no another character which prints U+22C5.

[UPDATE] This discussion is linked now with the Github issue thanks to @mlhetland. I would rather continue there, instead of discussing it here.

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**Author:** ![mlhetland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mlhetland/32/283_2.png) [@mlhetland](https://discourse.julialang.org/u/mlhetland)\
**Post date:** [July 18, 2018, 11:34am UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/7 "2018-07-18T11:34:55Z")

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I agree that U+00b7 is convenient to type, and I’ve wanted to use it as `\cdot` before as well. I don’t know how easily U+0387 is accessible on Greek keyboards – but I agree that if it is, we might to map it similarly. The fact that U+00b7 and U+0387 are “canonically the same,” Unicode-wise (as I understand it – and according to current Julia normalization) argues in favor of treating them the same way. Officially (according to UAX#31), that seems to mean that they should both be identifier characters, but since only one of them is, we’re not really in compliance with that, anyway, I guess?

At the very least, it seems odd to me that we normalize identifiers written with a valid identifier character into one containing an invalid identifier character – especially when it seems to be in violation of the motivation behind it (i.e., to comply with UAX#31).

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<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [July 18, 2018, 2:33pm UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/8 "2018-07-18T14:33:05Z")

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> [@mlhetland](#):
>
> Actually, it is even normalized to the middle dot when parsed as a symbol

Oh, good catch. This is because Julia symbols are NFC-normalized, and the NFC of [U+0387](http://www.fileformat.info/info/unicode/char/0387/index.htm) is U+00b7. Given this, it is crazy to treat the two points differently in identifiers.

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**Author:** ![mlhetland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mlhetland/32/283_2.png) [@mlhetland](https://discourse.julialang.org/u/mlhetland)\
**Post date:** [July 18, 2018, 4:10pm UTC](https://discourse.julialang.org/t/why-is-greek-ano-teleia-a-valid-identifier-character/12442/9 "2018-07-18T16:10:41Z")

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Solved in [PR #28167](https://github.com/JuliaLang/julia/pull/28167).