LALR
MyRpg use the lang! macro to collect essential grammar details and build LALR parsing table AT COMPILE TIME.
The lexical analysis is proceeded along with parsing, instead of pre-collecting all the tokens.
MyRpg supports subscribing multiple parsing events, which makes it more flexible:
Triggers when a new token was generated by lexer.
<terminal> => <regex> => |tok: Token| -> Option<Token> {
// do something with tok
Some(tok) // or None
}Triggers when a production was reduced by parser.
<non-terminal> => [
[ <symbol> ] => @reduce |ast: &mut Ast<_>| -> () {
// do something with ast
}
]Triggers when the parsing job finishes successfully. Make a traversal over the AST.
<non-terminal> => [
[ <symbol> ] => |/* match this production */| -> () {
// do something with ast
}
]This function is marked as returning Option<ValueType>, in case some node doesn't return anything. As a result, this function has it's default behaviour: expand all child ASTs and return the last's value.
Note that current AST node will be automatically destructured into children, so the function parameters must match your production declaration, e.g:
Expr "+" Term => |lhs, _, rhs| -> _ {
Some(lhs.gen().unwrap() + rhs.gen().unwrap())
}If you override this function, you have to call ast.gen() manually to traverse child ASTs.
use myrpg::{ast::*, LRParser, *};
lang! {
Name = MathExpr
ValueType = i32
;;
Number => r"[0-9]+",
Id => r"[a-zA-Z_]+"
;;
S => [
Expr => |child| -> _ {
let res = child.gen().unwrap();
println!("{:?}", child);
Some(res)
}
],
Expr => [
Expr "+" Term => |lhs, _, rhs| -> _ {
Some(lhs.gen().unwrap() + rhs.gen().unwrap())
},
Expr "-" Term => |lhs, _, rhs| -> _ {
Some(lhs.gen().unwrap() - rhs.gen().unwrap())
},
Term => |child| -> _ {
child.gen()
}
],
Term => [
Term "*" Factor => |lhs, _, rhs| -> _ {
Some(lhs.gen().unwrap() * rhs.gen().unwrap())
},
Term "/" Factor => |lhs, _, rhs| -> _ {
Some(lhs.gen().unwrap() / rhs.gen().unwrap())
},
Factor => |child| -> _ {
child.gen()
}
],
Factor => [
Number => |tok| -> Option<i32> {
Some(tok.val.parse().unwrap())
},
"(" Expr ")" => |_, child, _| -> _ {
child.gen()
}
]
}
#[test]
fn test_mathexpr() {
let parser = LRParser::<MathExpr>::new();
let res = parser.parse("4 * (2 + 1)");
println!("{:?}", res.unwrap().gen());
}use myrpg::{ast::*, LRParser, *};
lang! {
Name = IfExpr
ValueType = i32
;;
Id => r"[a-zA-Z_]+"
;;
S => [
Stmt
],
Stmt => [
"if" Id Stmt "else" Stmt,
"if" Id Stmt,
Id
]
}
#[test]
fn test_ifexpr() {
let parser = LRParser::<IfExpr>::new();
match parser.parse("if a b else c") {
Ok(val) => println!("{:?}", val),
Err(err) => println!("{:?}", err),
}
}Ready, under construction.
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