Easiest way to get started is through gll-macros:
toml
[dependencies]
gll = "0.0.1"
gll-macros = "0.0.1"
```rust
extern crate gll; extern crate gll_macros; ```
As an example, this is what you might write for a JSON-like syntax,
that uses plain identifiers instead of string literals for field names,
and allows values to be parenthesized Rust expressions:
rust
mod json_like {
::gll_macros::proc_macro_parser! {
Value =
Null:"null" |
False:"false" |
True:"true" |
Literal:LITERAL |
Array:{ "[" elems:Value* % "," "]" } |
Object:{ "{" fields:Field* % "," "}" } |
InterpolateRust:{ "(" TOKEN_TREE+ ")" };
Field = name:IDENT ":" value:Value;
}
}
You can also use a build script to generate the parser (TODO: document).
To parse a string with that grammar:
rust
let tokens = string.parse().unwrap();
json_like::Value::parse_with(tokens, |parser, result| {
let value = result.unwrap();
// ...
});
All grammars contain a set of named rules, with the syntax Name = rule;.
(the order between the rules doesn't matter)
Rules are made out of:
* grouping, using {...}
* string literals, matching input characters / tokens exactly
* character ranges: 'a'..='d' is equivalent to "a"|"b"|"c"|"d"
* only in scannerless mode
* builtin rules: IDENT, PUNCT, LITERAL, TOKEN_TREE
* only in proc macro mode
* named rules, referred to by their name
* concatenation: A B - "A followed by B"
* alternation: A | B - "either A or B"
* optionals: A? - "either A or nothing"
* lists: A* - "zero or more As", A+ - "one or more As"
* optional separator: A* % "," - "comma-separated As"
Parts of a rule can be labeled with field names, to allow later access to them:
LetDecl = "let" pat:Pat { "=" init:Expr }? ";"; produces:
rust
// Note: generic parameters omitted for brevity.
struct LetDecl {
pat: Handle<Pat>,
init: Option<Handle<Expr>>,
}
One Rust-specific convention is that alternation fields are enum variants.
Expr = Lit:LITERAL | Add:{ a:Expr "+" b:Expr }; produces:
rust
enum Expr {
Lit(Handle<LITERAL>),
Add {
a: Handle<Expr>,
b: Handle<Expr>,
},
}
Licensed under either of
at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.