fn num(n: i64) -> Value {

    Value::Number(Fraction::from_integer(n))

}

fn frac(n: i64, d: i64) -> Value {

    Value::Number(Fraction::new(n, d))

}

    fn test_type_names() {

        let cases = [

            (Value::Nil, "nil"),

            (Value::T, "boolean"),

            (num(42), "number"),

            (Value::String("hello".into()), "string"),

            (Value::Symbol("x".into()), "symbol"),

            (

                Value::Pair(Box::new(Pair::new(Value::Nil, Value::Nil))),

                "pair",

            ),

            (Value::Vector(vec![]), "vector"),

            (Value::Closure(Closure::new(0, vec![])), "closure"),

        ];

        for (value, expected_type) in cases {

            assert_eq!(value.type_name(), expected_type);

    }

    fn test_truthiness() {

        assert!(Value::Nil.is_nil());

        let truthy = [

            Value::T,

            num(0),

            num(1),

            Value::String(String::new()),

            Value::String("hello".into()),

            Value::Symbol("x".into()),

            Value::Pair(Box::new(Pair::new(Value::Nil, Value::Nil))),

            Value::Vector(vec![]),

            Value::Closure(Closure::new(0, vec![])),

        ];

        for val in truthy {

            assert!(!val.is_nil(), "{val:?} should be truthy");

    }

    fn test_fraction_equality() {

        assert_eq!(frac(1, 2), frac(2, 4));

        assert_eq!(frac(3, 6), frac(1, 2));

        assert_eq!(frac(100, 100), num(1));

    }

    fn test_fraction_normalization() {

        let half = Fraction::new(1, 2);

        let also_half = Fraction::new(50, 100);

        assert_eq!(half, also_half);

        let negative = Fraction::new(-1, 2);

        let also_negative = Fraction::new(1, -2);

        assert_eq!(negative, also_negative);

    }

    fn test_cons() {

        let pair = Pair::cons(num(1), num(2));

        match pair {

            Value::Pair(p) => {

                assert_eq!(p.car, num(1));

                assert_eq!(p.cdr, num(2));

    }

    fn test_nested_pairs() {

        let inner = Pair::cons(num(2), num(3));

        let outer = Pair::cons(num(1), inner);

        match outer {

            Value::Pair(p) => {

                assert_eq!(p.car, num(1));

                match p.cdr {

                    Value::Pair(inner_p) => {

                        assert_eq!(inner_p.car, num(2));

                        assert_eq!(inner_p.cdr, num(3));

    }

    fn test_empty_list() {

        let list = Value::Nil;

        let vec = list_to_vec(&list).unwrap();

        assert!(vec.is_empty());

        let back = vec_to_list(vec);

        assert_eq!(back, Value::Nil);

    }

    fn test_single_element_list() {

        let list = Pair::cons(num(42), Value::Nil);

        let vec = list_to_vec(&list).unwrap();

        assert_eq!(vec, vec![num(42)]);

        let back = vec_to_list(vec);

        assert_eq!(back, list);

    }

    fn test_multi_element_list() {

        let list = Pair::cons(num(1), Pair::cons(num(2), Pair::cons(num(3), Value::Nil)));

        let vec = list_to_vec(&list).unwrap();

        assert_eq!(vec, vec![num(1), num(2), num(3)]);

        let back = vec_to_list(vec);

        assert_eq!(back, list);

    }

    fn test_improper_list() {

        let improper = Pair::cons(num(1), num(2));

        assert!(list_to_vec(&improper).is_none());

        let improper = Pair::cons(num(1), Pair::cons(num(2), num(3)));

        assert!(list_to_vec(&improper).is_none());

    }

    fn test_heterogeneous_list() {

        let list = Pair::cons(

            num(1),

            Pair::cons(

                Value::String("hello".into()),

                Pair::cons(Value::T, Value::Nil),

        let vec = list_to_vec(&list).unwrap();

        assert_eq!(vec.len(), 3);

        assert_eq!(vec[0], num(1));

        assert_eq!(vec[1], Value::String("hello".into()));

        assert_eq!(vec[2], Value::T);

    }

    fn test_nested_list() {

        let inner = Pair::cons(num(2), Pair::cons(num(3), Value::Nil));

        let outer = Pair::cons(num(1), Pair::cons(inner.clone(), Value::Nil));

        let vec = list_to_vec(&outer).unwrap();

        assert_eq!(vec.len(), 2);

        assert_eq!(vec[0], num(1));

        assert_eq!(vec[1], inner);

    }

    fn test_roundtrip_preserves_structure() {

        let original = vec![num(1), Value::String("test".into()), Value::Nil, frac(1, 3)];

        let as_list = vec_to_list(original.clone());

        let back = list_to_vec(&as_list).unwrap();

        assert_eq!(original, back);

    }

    fn test_symbol_creation() {

        let sym = Symbol::new("foo", SymbolKind::Variable);

        assert_eq!(sym.name(), "foo");

        assert_eq!(sym.kind(), SymbolKind::Variable);

    }

    fn test_symbol_table() {

        let mut table = SymbolTable::new();

        table.define(Symbol::new("+", SymbolKind::Operator));

        table.define(Symbol::new("car", SymbolKind::Native));

        assert!(table.contains("+"));

        assert!(table.contains("car"));

        assert!(!table.contains("undefined"));

        assert_eq!(table.lookup("+").unwrap().kind(), SymbolKind::Operator);

        assert_eq!(table.lookup("car").unwrap().kind(), SymbolKind::Native);

    }

    fn test_symbol_table_builtins() {

        let table = SymbolTable::with_builtins();

        assert!(table.contains("+"));

        assert!(table.contains("IF"));

        assert!(table.contains("CAR"));

        assert_eq!(table.lookup("+").unwrap().kind(), SymbolKind::Operator);

        assert_eq!(table.lookup("IF").unwrap().kind(), SymbolKind::SpecialForm);

        assert_eq!(table.lookup("CAR").unwrap().kind(), SymbolKind::Native);

    }

    fn test_closure_creation() {

        let closure = Closure::new(42, vec![num(1), num(2)]);

        assert_eq!(closure.code_id, 42);

        assert_eq!(closure.env, vec![num(1), num(2)]);

    }

    fn test_empty_closure() {

        let closure = Closure::new(0, vec![]);

        assert_eq!(closure.code_id, 0);

        assert!(closure.env.is_empty());

    }

    fn test_long_list() {

        let values: Vec<Value> = (0..1000).map(num).collect();

        let list = vec_to_list(values.clone());

        let back = list_to_vec(&list).unwrap();

        assert_eq!(values, back);

    }

    fn test_deeply_nested_pairs() {

        let mut val = num(0);

        for i in 1..100 {

            val = Pair::cons(num(i), val);

        }

        match &val {

            Value::Pair(p) => assert_eq!(p.car, num(99)),

    }

    fn test_large_vector() {

        let vec: Vec<Value> = (0..10000).map(num).collect();

        let val = Value::Vector(vec.clone());

        match val {

            Value::Vector(v) => assert_eq!(v.len(), 10000),

    }