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Macro future proofing #550
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# Unresolved questions | ||
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1. What should the FOLLOW sets for `item`, `path`, and `meta` be? | ||
2. Should the `FOLLOW` set for `ty` be extended? In practice, `RArrow`, |
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Forgot one, of course: =
Oh, and a massive +1 to the overall idea here. |
+1, I'm convinced this is necessary. Detailed futures of some NTs are a bit unclear, though. |
@cmr are there any changes you'd like to make to this RFC before we merge it? |
@nick29581 maybe. The algorithm here no longer reflects the implementation, and the follow sets are subtly incorrect. |
@cmr Ok, ping me when you are happy and I'll merge it |
@nick29581 this is ready. |
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- `FOLLOW(pat)` = `{FatArrow, Comma, Eq}` | ||
- `FOLLOW(expr)` = `{FatArrow, Comma, Semicolon}` | ||
- `FOLLOW(ty)` = `{Comma, FatArrow, Colon, Eq, Gt, Ident(as)}` |
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@cmr, was there a reason for not including Semicolon on this list as well?
It's handy when defining matchers like $( fn $n:ident( $(p:ident : $t:ty),* ) -> $r:ty ; )*
(note the trailing 'ty')
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No, that was indeed an oversight
sent from my phone
On Jan 23, 2015 12:24 AM, "Vadim Chugunov" [email protected] wrote:
In text/0000-macro-future-proofing.md
#550 (comment):
continue, else, reject.
- If
T
has the form$(...)U+
or$(...)U*
for some tokenU
, runthe algorithm on the contents with `F` set to `U`. If it accepts,
check that the last token in the sequence can be followed by `F`. If
so, accept. Otherwise, reject.
+This algorithm should be run on every matcher in every
macro_rules
+invocation, withF
asEOF
. If it rejects a matcher, an error should be
+emitted and compilation should not complete.
+
+The current legal fragment specifiers are:item
,block
,stmt
,pat
,
+expr
,ty
,ident
,path
,meta
, andtt
.
+
+-FOLLOW(pat)
={FatArrow, Comma, Eq}
+-FOLLOW(expr)
={FatArrow, Comma, Semicolon}
+-FOLLOW(ty)
={Comma, FatArrow, Colon, Eq, Gt, Ident(as)}
@cmr https://github.com/cmr, was there a reason for not including
Semicolon on this list as well?
It's handy when defining matchers like $( fn$n:ident( $ (p:ident :
$t:ty),* ) -> $r:ty ; )* (note the trailing 'ty')—
Reply to this email directly or view it on GitHub
https://github.com/rust-lang/rfcs/pull/550/files#r23432570.
(RFC was accepted and has been heavily amended since; current text is: https://github.com/rust-lang/rfcs/blob/master/text/0550-macro-future-proofing.md )
Rendered
Implementation: https://github.com/cmr/rust/tree/macro-input-future-proofing