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Corrected EBNF grammar in the manual #14277

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May 20, 2014
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Corrected EBNF grammar in the manual #14277

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18 changes: 9 additions & 9 deletions src/doc/rust.md
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Original file line number Diff line number Diff line change
Expand Up @@ -848,11 +848,11 @@ extern crate foo = "some/where/rust-foo#foo:1.0"; // a full crate ID for externa
##### Use declarations

~~~~ {.notrust .ebnf .gram}
use_decl : "pub" ? "use" ident [ '=' path
| "::" path_glob ] ;
use_decl : "pub" ? "use" [ ident '=' path
| path_glob ] ;
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Um… what? These changes would make use; valid, which it is certainly not. A use statement must be followed by an identifier.

The grammar already existing appears to me to be correct.

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I take back what I said about the grammar existing being correct—I’ve been reading other grammar rules too much recently (the IETF RFC ones in particular) and was thinking […] meant optional. There is a problem with the current grammar, but the new one is wrong also. I think that just tacking a question mark after the ] on the existing grammar would be correct? OK, OK, that responsibility got shifted to the path_glob rule… not doing well today, am I?

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My line of thought is that a single identifier is also a path. path_glob can match multiple paths.

// Valid declarations
use ident = simple::path;
use simple::path;
use {many, idents}; // doesn't start with an ident!
// Invalid
use simple::path = another::path;
use *;
use;


path_glob : ident [ "::" path_glob ] ?
| '*'
path_glob : ident [ "::" [ path_glob
| '*' ] ] ?
| '{' ident [ ',' ident ] * '}' ;
~~~~

Expand Down Expand Up @@ -1743,7 +1743,7 @@ import public items from their destination, not private items.
attribute : '#' '!' ? '[' meta_item ']' ;
meta_item : ident [ '=' literal
| '(' meta_seq ')' ] ? ;
meta_seq : meta_item [ ',' meta_seq ]* ;
meta_seq : meta_item [ ',' meta_seq ] ? ;
~~~~

Static entities in Rust — crates, modules and items — may have _attributes_
Expand Down Expand Up @@ -3027,11 +3027,11 @@ then any `else` block is executed.
### Match expressions

~~~~ {.notrust .ebnf .gram}
match_expr : "match" expr '{' match_arm [ '|' match_arm ] * '}' ;
match_expr : "match" expr '{' match_arm * '}' ;

match_arm : match_pat "=>" [ expr "," | '{' block '}' ] ;
match_arm : attribute * match_pat "=>" [ expr "," | '{' block '}' ] ;

match_pat : pat [ ".." pat ] ? [ "if" expr ] ;
match_pat : pat [ '|' pat ] * [ "if" expr ] ? ;
~~~~

A `match` expression branches on a *pattern*. The exact form of matching that
Expand Down Expand Up @@ -3137,7 +3137,7 @@ using the `ref` keyword,
or to a mutable reference using `ref mut`.

Subpatterns can also be bound to variables by the use of the syntax
`variable @ pattern`.
`variable @ subpattern`.
For example:

~~~~
Expand Down