4 ms·

I mean, obviously that one should only appear within Mongolian text and not within indentation. To state explicitly what should be implicitly obvious, there is

by rmunn 1mo ago

I mean, obviously that one should only appear within Mongolian text and not within indentation. To state explicitly what should be implicitly obvious, there is no valid reason (that I'm aware of, I welcome any non-facetious correction) to use any character except U+0009 and U+0020 within indentation. Horizontal Record Separator? Zero-width joiner? Language-specific whitespace characters like your example? All make sense within human text (well, maybe not HRS), but in programming, they should be eschewed in favor of the characters that can be typed in every single keyboard layout in the world. Even languages that don't put spaces between words, such as Thai, still put spaces between sentences (or comma phrases) and therefore keep the space bar in their keyboard layout. And since mixing tabs and spaces (even between lines, where some lines are tab-indented and some are space-indented) creates problems for whitespace-sensitive language, there's a reason why every whitespace-sensitive language I'm aware of has tended to either outright forbid, or at least discourage, U+0009 and its ambiguous meaning (since its meaning isn't clear until you know people's editor configurations, which are usually not available to the validation code running in CI or on other people's machines).

fc417fc802 1mo ago
> To state explicitly what should be implicitly obvious, there is no valid reason ... There doesn't need to be an articulable reason. Or rather there's generally no expectation that a central authority will be able to reliably enumerate such. Everything should default to being permitted and only ever be restricted for good reason. But since you asked. U+2003 for example carries formatting information. Maybe an editor could be written (or even already exists) that would find that useful. Who is any third party to dictate that? U+00A0 similarly communicates information about the desired formatting and I can see no reason it would be unreasonable for someone to use it nor why its use should pose a technical challenge to a compiler. > creates problems for whitespace-sensitive langauge Does it? That seems like an invented problem to me. You have a running prefix composed of arbitrary whitespace characters. Any change in that prefix is a change in the level of indentation. You can add or remove arbitrary amounts from the end of the prefix. In the event you remove from it the result must exactly match the previous stack level. What's so complicated about this? > outright forbid, or at least discourage, U+0009 and its ambiguous meaning (since its meaning isn't clear until you know people's editor configurations ... Did you mix up your code points there? It's space that's ambiguous, not tab. Regardless I think that a compiler worrying about the specifics of text editors or other tooling would be backward information flow and a massive abstraction violation. Semantic meaning is entirely dictated by the compiler, not the other way around. There's no convincing reason (IMO) to impose restrictions that aren't technically necessary or to otherwise needlessly employ solutions that would reduce generalization.
- rmunn 1mo ago
  > Did you mix up your code points there? It's space that's ambiguous, not tab. Space is always the same width, but tab means a variable number of spaces (usually either 4 or 8, but I've seen 3 before) depending on people's editor configuration. What makes you say that the space character, U+0020, is ambiguous?
  - fc417fc802 1mo ago
    A single tab always indicates (AFAIK, in common usage) a single level of indentation. Whereas depending on editor configuration a single level of indentation could be represented by any number of spaces - commonly somewhere between 4 and 8, but who can say? Tab never "means" any number of spaces. How it gets displayed varies but the meaning (of any character, not just tab) can only ever be determined by usage, not display choices (at least for any sane way of doing things). Otherwise what would you make of escape sequences or binary files? Or constructs such as a nonbreaking space? What business does a compiler have worrying about display width? As I said earlier worrying about the specifics of the editor or other tooling would be backwards information flow and a massive abstraction violation. What if I choose to program in a variable width font? (For the record writing that left me feeling disgusted.)
    - zephen 1mo ago
      Truly, indentation is the moveable feast. Even on ancient typewriters, you could adjust your tabs depending on what you are doing. And people who have dissimilar tastes in tabbage will certainly write stuff that doesn't appear that great in each others' editors. > What business does a compiler have worrying about display width? The business of the compiler is to insure that code that it deems acceptable is not ambiguous to different users. Since people can set their own tab spacing, display of tabs is, in an indentation-sensitive language, inherently ambiguous. > What if I choose to program in a variable width font? As long as the spacing of any prepended whitespace doesn't arbitrarily change depending on the phase of the moon, the compiler shouldn't (and Python doesn't) give a rat's ass about your display preferences. The only important thing here is that the location of the left margin on every line is meaningful, both to the compiler, and to any viewers of your code.

by rmunn 1mo ago

fc417fc802 1mo ago

> To state explicitly what should be implicitly obvious, there is no valid reason ... There doesn't need to be an articulable reason. Or rather there's generally no expectation that a central authority will be able to reliably enumerate such. Everything should default to being permitted and only ever be restricted for good reason. But since you asked. U+2003 for example carries formatting information. Maybe an editor could be written (or even already exists) that would find that useful. Who is any third party to dictate that? U+00A0 similarly communicates information about the desired formatting and I can see no reason it would be unreasonable for someone to use it nor why its use should pose a technical challenge to a compiler. > creates problems for whitespace-sensitive langauge Does it? That seems like an invented problem to me. You have a running prefix composed of arbitrary whitespace characters. Any change in that prefix is a change in the level of indentation. You can add or remove arbitrary amounts from the end of the prefix. In the event you remove from it the result must exactly match the previous stack level. What's so complicated about this? > outright forbid, or at least discourage, U+0009 and its ambiguous meaning (since its meaning isn't clear until you know people's editor configurations ... Did you mix up your code points there? It's space that's ambiguous, not tab. Regardless I think that a compiler worrying about the specifics of text editors or other tooling would be backward information flow and a massive abstraction violation. Semantic meaning is entirely dictated by the compiler, not the other way around. There's no convincing reason (IMO) to impose restrictions that aren't technically necessary or to otherwise needlessly employ solutions that would reduce generalization.

rmunn 1mo ago
> Did you mix up your code points there? It's space that's ambiguous, not tab. Space is always the same width, but tab means a variable number of spaces (usually either 4 or 8, but I've seen 3 before) depending on people's editor configuration. What makes you say that the space character, U+0020, is ambiguous?
- fc417fc802 1mo ago
  A single tab always indicates (AFAIK, in common usage) a single level of indentation. Whereas depending on editor configuration a single level of indentation could be represented by any number of spaces - commonly somewhere between 4 and 8, but who can say? Tab never "means" any number of spaces. How it gets displayed varies but the meaning (of any character, not just tab) can only ever be determined by usage, not display choices (at least for any sane way of doing things). Otherwise what would you make of escape sequences or binary files? Or constructs such as a nonbreaking space? What business does a compiler have worrying about display width? As I said earlier worrying about the specifics of the editor or other tooling would be backwards information flow and a massive abstraction violation. What if I choose to program in a variable width font? (For the record writing that left me feeling disgusted.)
  - zephen 1mo ago
    Truly, indentation is the moveable feast. Even on ancient typewriters, you could adjust your tabs depending on what you are doing. And people who have dissimilar tastes in tabbage will certainly write stuff that doesn't appear that great in each others' editors. > What business does a compiler have worrying about display width? The business of the compiler is to insure that code that it deems acceptable is not ambiguous to different users. Since people can set their own tab spacing, display of tabs is, in an indentation-sensitive language, inherently ambiguous. > What if I choose to program in a variable width font? As long as the spacing of any prepended whitespace doesn't arbitrarily change depending on the phase of the moon, the compiler shouldn't (and Python doesn't) give a rat's ass about your display preferences. The only important thing here is that the location of the left margin on every line is meaningful, both to the compiler, and to any viewers of your code.