use crate::sexpr::{self, Atom, Expr};

#[derive(Debug, Clone)]
pub struct Rule {
    pub lhs: Expr,
    pub rhs: Expr
}

impl TryFrom<Expr> for Rule {
    type Error = ();
    fn try_from(value: Expr) -> Result<Self, Self::Error> {
        if let Expr::Application(v) = value && v[0] == Expr::Atom(Atom::Builtin(String::from("def-rule"))) && v.len() == 3 {
            Ok(Rule {
                lhs: v[1].clone(),
                rhs: v[2].clone()
            })
        } else {Err(())}
    }
}

pub fn parse_def_rules(input: String) -> Vec<Rule> {
    let exprs = sexpr::Parser::new(&input).parse_all();
    exprs.iter().filter_map(|e| e.clone().try_into().ok()).collect()
}