fn sym(name: &str) -> Expr {

    Expr::Symbol(name.into())

}

fn nil_and_the_empty_list_print_as_nil() {

    assert_eq!(format_expr(&Expr::Nil), "nil");

    assert_eq!(format_expr(&Expr::List(vec![])), "nil");

    assert_eq!(format_runtime_value(&Value::Nil), "nil");

}

fn a_cons_chain_ending_in_nil_prints_as_a_proper_list() {

    assert_eq!(format_expr(&Expr::cons(sym("A"), Expr::Nil)), "(A)");

    assert_eq!(

        format_expr(&Expr::cons(sym("A"), Expr::cons(sym("B"), Expr::Nil))),

}

fn a_cons_chain_ending_in_an_atom_keeps_its_dot() {

    assert_eq!(format_expr(&Expr::cons(sym("A"), sym("B"))), "(A . B)");

    assert_eq!(

        format_expr(&Expr::cons(sym("A"), Expr::cons(sym("B"), sym("C")))),

}