consider making `in` a contextual keyword

[thestinger]

The statement for pattern in iterator { ... } only uses in as a separator for humans. It could just as easily be <- like Scala, so I don't see a good reason to reserve such a common word.

[emberian]

+1, I don't really understand the aversion to having contextual keywords.

[emberian]

(And if we have nested comments, haven't we already lost that battle?)

[chris-morgan]

Syntax highlighters will hate this; without a full parse (which most highlighters cannot do and the rest probably should not do), it will be impossible to say whether in is being used as a keyword or as an identifier.

[emberian]

Surely it can "know" if it is expecting a for loop or not? /me does not
have much experience in such realms

On Wed, Dec 4, 2013 at 10:53 PM, Chris Morgan notifications@github.comwrote:

Syntax highlighters will hate this; without a full parse (which most
highlighters cannot do and the rest probably should not do), it will be
impossible to say whether in is being used as a keyword or as an
identifier.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/10816#issuecomment-29869639
.

[thestinger]

@chris-morgan: Syntax highlighters don't need to highlight in. It only occurs as an arbitrary separator in for loops.

[chris-morgan]

@cmr Nested comments are quite a different problem and much easier to do properly. (OK, I'll admit the comment nesting I put in the Vim syntax yesterday is not perfect, but that's because of a slight parsing concept mismatch in Vim where it allows a contained region to open, interrupting a close match—hence /* */* is highlighted as two levels deep rather than the * being out of the comment.)

@cmr It can be approximated, but not done perfectly without a considerably more complex and computationally heavy (i.e. slow, which is probably not acceptable for a text editor) architecture. (Being pat rather than expr makes it a little bit less problematic, but doing it correctly still requires an absolute minimum of parsing all braces, brackets and parentheses in the syntax file.)

@thestinger As a generalisation, syntax highlighters highlight all keywords; in for $pat in $expr, in is a keyword, so people will expect in to be highlighted.

[liigo]

For … in … is OK to me, <- is ugly
在 2013年12月5日 上午11:42，"Daniel Micay" notifications@github.com写道：

The expression for pattern in iterator only uses in as a separator for
humans. It could just as easily be <- like Scala, so I don't see a good
reason to reserve such a common word.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/10816
.

[liigo]

and for...in is also used in several languages, is user-friendly. But for <-, you just push to users another Strange-Symbols, non-meaningful, a bit ugly.

[thestinger]

Closing, because this needs to go through rust-rfcs.