streamy | Stream your own music from ur browser | Audio Utils library

Solution 1) You should start server using

It was a problem with the .eslintrc configuration as @DrewReese suspected. The plugins array was missing react-hooks and the rules object was missing react-hooks rules.

So, the final configuration is as follows-

I’d use something like this:

First, you should know that Heroku doesn't allow to expose multiple ports, which means you should change the approach of multiple ports to something else (see this answer).

Second, the file client/src/apis/streams.js is hard-coded configured to send requests to http://localhost:4000/ - which is not a good idea.
Whatever approach you choose - even deploying to another host server - you will need to dynamically configure the API endpoint, per environment.

I would also recommend you to:

1. Change the way you deploy react, as explained here.
2. After doing the above, consider consolidating your API service with the static server, so that you don't need multiple ports, and then everything becomes easier.

You are looking for Stream.mapToInt(), which creates an IntStream and IntStream.sum(). You can try this:

It seems that there isn't a way to avoid the newtype. The Backpack thesis clearly states that type synonyms are required to be nullary (section 6.2.4 "Subtyping rules"):

the implementing type synonyms are required to be nullary: for example, type M a = a is not a valid implementation of the abstract data M a, but type M = Maybe :: * -> * is. This restriction stems from an old design decision in Haskell to not support type level lambdas. This restriction greatly helps type inference, since given the type equality t a = s b, we can now conclude that t = s and a = b (this property is called generativity).

Also related, in section B.2 "Challenges":

Translucency: A feature not supported in Backpack’14 but supported in Backpack’17 is the ability to use a type synonym to implement an abstract data type. This introduces a form of “translucency”, where the abstract data type is opaque while the implementation is unknown, and transparent afterwards. For example, in Section 2.3, we demonstrated how we could instantiate a generic regular expression matcher to match on strings. Inside the implementation of the matcher, we knew nothing about the abstract type Str; after instantiating it, the accept function transparently accepts String arguments.

I recommend to use a variable to store the size, as there is several places that requires it : maxSize

1. You can join your elements with a return line, and then print, and as a tip you can simplify your use of StringBuilder with a map operation