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fn lift(comptime x: anytype) type {
    return struct {
        pub const value = x;
    };
}

fn integers(comptime int: comptime_int) type {
    return struct {
        pub const car = lift(int);
        pub const cdr = integers(int + 1);
    };
}

fn zip(comptime l: type) fn (comptime r: type) type {
    return struct {
        fn next(comptime r: type) type {
            return struct {
                pub const car = struct {
                    pub const car = l.car;
                    pub const cdr = r.car;
                };

pub const cdr = if (l.cdr == void or r.cdr == void) void else zip(l.cdr)(r.cdr);
            };
        }
    }.next;
}

fn repeatN(comptime count: comptime_int) fn (comptime value: anytype) type {
    return struct {
        fn next(comptime value: anytype) type {
            if (count == 0) return void;
            return struct {
                pub const car = lift(value);
                pub const cdr = repeatN(count - 1)(value);
            };
        }
    }.next;
}

fn foldr(comptime f: type) fn (comptime init: type) fn (comptime list: type) type {
    return struct {
        fn next(comptime init: type) fn (comptime list: type) type {
            return struct {
                fn next(comptime list: type) type {
                    return if (list == void) init else f.value(list.car)(foldr(f)(init)(list.cdr));
                }
            }.next;
        }
    }.next;
}

fn first(comptime pair: type) @TypeOf(pair.car) {
    return pair.car;
}

fn cons(comptime a: type) fn (comptime b: type) type {
    return struct {
        fn next(comptime b: anytype) type {
            return struct {
                pub const car = a;
                pub const cdr = b;
            };
        }
    }.next;
}

comptime {
    var list = flatten(zip(integers(0))(repeatN(10)({})));
    while (list != void) : (list = list.cdr) {
        @compileLog(list.car.value);
    }
}