Or you just forbid mixing spaces and tabs in the same indentation sequence, the way most whitespace-sensitive languages seem to end up doing. Or you make a slightly more reasonable rule: spaces may follow tabs, but no tabs may follow a space. That's at least unambiguous.

▲

fc417fc802 an hour ago | parent [-]

But it also feels arbitrary and annoyingly restrictive. On top of that there are at least 25 whitespace codepoints in UTF. Should your language really be opinionated about when, where, and in what order (for example) the "mongolian vowel separator" appears?

▲

rmunn 40 minutes ago | parent | next [-]

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 langauge, 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).

▲

Mogzol an hour ago | parent | prev [-]

> and annoyingly restrictive

How so? In what scenario would you ever need to use a sequence like <tab><space><tab> in indentation in your source code? Let alone using esoteric Unicode whitespace characters for indentation. I think it is perfectly reasonable for the language to make the restriction that indentation must be either all tabs, tabs followed by spaces, or all spaces.

	▲	fc417fc802 18 minutes ago \| parent [-]
		> In what scenario would you ever need to use a sequence like <tab><space><tab> in indentation in your source code? Writing a lisp in an editor that doesn't do boneheaded things with tabs? That's the only one I've personally run into but lack of imagination is hardly a good excuse to implement arbitrary restrictions. > Let alone using esoteric Unicode whitespace characters for indentation. How do you know what's esoteric in other countries? I certainly don't. I'm not an expert in linguistics but I'm sure that people everywhere in the world write computer programs at this point. > I think it is perfectly reasonable ... Without any concrete justification? Why would entirely artificial restrictions ever be seen as reasonable?