type Context = i32;

fn run_sync_1(ctx: Context, next: &Fn(Context) -> Context) -> Context {
    let ctx_new = ctx + 1;

    next(ctx_new)
}

fn run_sync_2(ctx: Context, next: &Fn(Context) -> Context) -> Context {
    let ctx_new = ctx * 2;

    next(ctx_new)
}

fn run_sync_3(ctx: Context, _next: &Fn(Context) -> Context) -> Context {
    ctx - 1
}

type ChainType<T> = fn(T, &Fn(T) -> T) -> T;

fn main() {
    // Type of impl Fn(Context, impl Fn(Context) -> Context) -> Context

    // Sets to 1
    fn chain_a(context: Context, end: &Fn(Context) -> Context) -> Context {
        run_sync_1(context, &|context| {
            run_sync_2(context, &|context| {
                run_sync_3(context, end)
            })
        })
    };
    let chain_1: ChainType<Context> = chain_a;

    // Adds 3
    fn chain_b(context: Context, end: &Fn(Context) -> Context) -> Context {
        run_sync_1(context, &|context| {
            run_sync_1(context, &|context| {
                run_sync_1(context, end)
            })
        })
    };
    let chain_2: ChainType<Context> = chain_b;

    // ((3 + 1) * 2) - 1 = 7
    println!("results: {}", chain_2(0, &|context| {
        chain_1(context, &|_| {
            panic!("Error!")
        })
    }));
}