#[macro_export]
macro_rules! primitive {
    ($env:expr, $arity:expr, $name:expr, $closure:expr) => {
        let val = crate::lisp::expr::LispExpr::PrimitiveFunc(crate::lisp::expr::PrimitiveFunc {
            arity: $arity,
            closure: $closure,
        });
        let _ = $env.insert($name.to_string(), val);
    };
}