The following notations are used by the Lexer and Syntax grammar snippets:
| Notation | Examples | Meaning |
|---|---|---|
| CAPITAL | KW_IF, INTEGER_LITERAL | A token produced by the lexer |
| ItalicCamelCase | LetStatement, Item | A syntactical production |
string |
x, while, * |
The exact character(s) |
| x? | pub? |
An optional item |
| x* | OuterAttribute* | 0 or more of x |
| x+ | MacroMatch+ | 1 or more of x |
| xa..b | HEX_DIGIT1..6 | a to b repetitions of x |
| Rule1 Rule2 | fn Name Parameters |
Sequence of rules in order |
| | | u8 | u16, Block | Item |
Either one or another |
| [ ] | [b B] |
Any of the characters listed |
| [ - ] | [a-z] |
Any of the characters in the range |
| ~[ ] | ~[b B] |
Any characters, except those listed |
~string |
~\n, ~*/ |
Any characters, except this sequence |
| ( ) | (, Parameter)? |
Groups items |
| U+xxxx | U+0060 | A single unicode character |
| <text> | <any ASCII char except CR> | An English description of what should be matched |
| Rule suffix | IDENTIFIER_OR_KEYWORD except crate |
A modification to the previous rule |
Sequences have a higher precedence than | alternation.
Some rules in the grammar — notably unary operators, binary operators, and keywords — are given in a simplified form: as a listing of printable strings. These cases form a subset of the rules regarding the token rule, and are assumed to be the result of a lexical-analysis phase feeding the parser, driven by a DFA, operating over the disjunction of all such string table entries.
When such a string in monospace font occurs inside the grammar,
it is an implicit reference to a single member of such a string table
production. See tokens for more information.
Below each grammar block is a button to toggle the display of a railroad diagram. A square element is a non-terminal rule, and a rounded rectangle is a terminal.
The following are common definitions used in the grammar.
r[input.syntax]
@root CHAR -> <a Unicode scalar value>
NUL -> U+0000
TAB -> U+0009
LF -> U+000A
CR -> U+000D