earlgrey

Use Earley's algorithm to retrieve all possible parses of an input given a grammar.

Example: ``` fn main() { use std::str::FromStr;

let grammar = r#"
    expr   := expr ('+'|'-') term | term ;
    term   := term ('*'|'/') factor | factor ;
    factor := '-' factor | power ;
    power  := ufact '^' factor | ufact ;
    ufact  := ufact '!' | group ;
    group  := num | '(' expr ')' ;
"#;

let input = "3.2 ^ 3 - (8 / 4)!";

let parser = earlgrey::ParserBuilder::new()
    .plug_terminal("num", |n| f64::from_str(n).is_ok())
    .treeficator("expr", &grammar);

for tree in parser(&mut Tokenizer::from_str(input)).unwrap() {
  tree[0].print();
}

} ```

earley references

• http://loup-vaillant.fr/tutorials/earley-parsing/
• https://user.phil-fak.uni-duesseldorf.de/~kallmeyer/Parsing/earley.pdf
• http://joshuagrams.github.io/pep/
• https://github.com/tomerfiliba/tau/blob/master/earley3.py