exercises | simple programs in C , Python , and Haskell

I think this does what you want, and hopefully there's an easier way. I think a puzzle piece you hadn't considered yet was "$mergeObjects".

What the spec means is that no code is run to clean up int i. It simply ceases to exist. Its memory is part of Foo and whenever a Foo instance is released, then i goes with it.

For pointers the same is true, the pointer itself will simply disappear (it's really just another number), but the pointer might point at something that needs to also be released. The compiler doesn't know if that is the case, so you have to write a destructor.

This is why things like std::shared_ptr exist; they are clever pointers (aka 'smart') and the compiler does know if it points at something that needs to be released and will generate the correct code to do so. This is why you should always use smart pointers instead of 'naked' ones (like int *p).

Let's take some List(a, b, c). After passing it into sequenceRight it will turn into:

Your problem is that your code don't uses Async all the way up.

Your Account class has the method Open, Close, Balance and Transaction and you use a AsyncReplyChannel but you use PostAndReply to send the message. This means: You send a message to the MailboxProcessor with a channel to reply. But, at this point, the method waits Synchronously to finish.

Even with Async.Parallel and multiple threads it can mean a lot of threads lock themsels. If you change all your Methods to use PostAndAsyncReply then your problem goes away.

There are two other performance optimization that can speed up performance, but are not critical in your example.

1. Calling the Length of a list is bad. To calculate the length of a list, you must go through the whole list. You only use this in Transaction to print the length, but consider if the transaction list becomes longer. You alway must go through the whole list, whenever you add a transaction. This will be O(N) of your transaction list.

2. The same goes for calling (List.sum). You have to calculate the current Balance whenever you call Balance. Also O(N).

As you have a MailboxProcessor, you also could calculate those two values instead of completly recalculating those values again and again.Thus, they become O(1) operations.

On top, i would change the Open, Close and Transaction messages to return nothing, as in my Opinion, it doesn't make sense that they return anything. Your examples even makes me confused of what the bool return values even mean.

In the Close message you return state.Opened before you set it to false. Why?

In the Open message you return the negated state.Opened. How you use it later it just looks wrong.

If there is more meaning behind the bool please make a distinct Discriminated Union out of it, that describes the purpose of what it returns.

You used an option throughout your code, i removed it, as i don't see any purpose of it.

Anyway, here is a full example, of how i would write your code that don't have the speed problems.

Please, try something like the following (I included comments within the code, I hope it makes it clear):

There is currently no way to express this in the type system.

I assume you mean min instead of max. The typical approach would be:

This problem has been resolved in a new version of the kotlinx-coroutines package (1.6.0-RC). See my github compare across branches. Tests now pass as expected with this version.

The for loop is exited if either c equals EOF or c equals '\n'. Therefore, immediately after the for loop, if you want to know which value c has, you must test.

In rust only the last expression is taken as return value.

In your case: