use std::rc::Rc;

#[derive(Debug, Eq, PartialEq)]
pub enum Form {
    Nil,
    Int(i32),
    Bool(bool),
    Symbol(String),
    Pair(Rc<Form>,Rc<Form>),
    PrimComb(String, fn(Rc<Form>, Rc<Form>) -> Rc<Form>),
    DeriComb { se: Rc<Form>, de: Option<String>, params: Rc<Form>, body: Rc<Form> },
}
impl Form {
    pub fn truthy(&self) -> bool {
        match self {
            Form::Bool(b) => *b,
            Form::Nil     => false,
            _             => true,
        }
    }
    pub fn int(&self) -> Option<i32> {
        match self {
            Form::Int(i) => Some(*i),
            _ => None,
        }
    }
    pub fn sym(&self) -> Option<&str> {
        match self {
            Form::Symbol(s) => Some(s),
            _ => None,
        }
    }
    pub fn car(&self) -> Option<Rc<Form>> {
        match self {
            Form::Pair(car, cdr) => Some(Rc::clone(car)),
            _ => None,
        }
    }
    pub fn cdr(&self) -> Option<Rc<Form>> {
        match self {
            Form::Pair(car, cdr) => Some(Rc::clone(cdr)),
            _ => None,
        }
    }
}