pos VS Wartremover

Make the changes to the code you just cloned in your computer. If you already have changes, you can copy-paste them into this local project whose code is being tracked by git. Then, using the GitHub terminal for Windows or the Linux/Mac terminal with the git command line command installed, from the directory of the repository you cloned (so for this example it would be ~/Home/code/pos because the name of my project is "pos") run git status to see the list of files you modified in this project. Then run git add . (with a period in the command) to add all the modified files or git add file.py to add say a file named file.py that you modified. Then run the command git commit -m "I modified the file file.py" or whatever you want to be the message documenting what change you made to your project (the -m flag specifies the commit message). A git commit is like a save point in a videogame, if you mess up you can always go back to it, reverting all your code to that point. Finally, do git push origin master to push your changes from your local git repository to the one in GitHub (in this command master refers to the name of the branch in the git repository, the master branch, and origin refers to the origin of where you got the code from, in this example it is https://github.com/JohnReedLOL/pos . A branch in git is like a version of your code and the master branch is the main version. If someone is working on version 2.0 they might make a branch named "2.0" that is a clone of the master branch, add their commits to it, and when they're done merge those commits back into the master branch.

A portfolio of personal projects ceases to matter when you have years of relevant experience but it can help you get your first few jobs. The code for personal projects is usually hosted on GitHub with a README.md file in your project's repository for documentation. Here's a project I published because I found it useful for print debugging Scala code: https://github.com/JohnReedLOL/pos . Usually if prospective employers look at your personal project they will just briefly look at the README documentation without actually running it (I don't think any employer actually takes the time to run the code in your personal projects). I also have a website I built for my mom's condo at https://sea-air-towers.herokuapp.com/ with the source code at https://github.com/JohnReedLOL/TypeScript-Node-Starter , both of which I previously put on my resume. I like having links to websites I built on my resume because a potential employer can click the link and briefly take a look, which is much more convenient for them than having to execute the code you wrote on their machine, which they don't have the time or interest in doing. For hosting I used Heroku because it's more convenient than AWS and they used to be 100% free for personal projects, but recently Salesforce bought Heroku and ended that policy so the app hosting has been costing $7 per month. You might incur less cost if you take out AWS free tier or free credits although those run out after some number of months.

By contrast, Java and ECMAScript are essentially what we might call "classical" imperative OOP languages, although ECMAScript reveals much more of its Lisp-inspired "map/filter/reduce" FP roots. IMO ESLint is essentially table stakes for working with ECMAScript, but honestly, I wouldn't stop there and would insist on working in TypeScript, including some of the tooling for ESLint specifically for TypeScript, dialing type-safety up to 11, effectively like using Wart Remover with Scala.

I'm awed by the maturity of the Scala 2 compiler. Every minor version in the 2.13 series adds a new linting improvement. You can see that if you have sbt-tpolecat in your project. I'm always happy to see that some option from Wartremover is no longer used.

I was recently trying to move away from Scapegoat to Wartremover and I got bitten by this bug which is particularly prevalent in codebases using Typelevel libraries.

There is also wartremover but you cannot run it separately from your compile command.

or `NonUnitStatements` without explicit annotation.

This effectively locks you into writing pure code (you can extend the linter to cover other things like not using `Future` or not using Java libs outside of `MonadError` from cats[4]). The linters operate on typed ASTs at compile time, and have plugins for the most popular scala build tools. Coupled with `-XFatalWarnings', you can guarantee that nothing unexpected happens unless you explicitly pop the escape hatch, for the most part.

You can still bring in external libraries that haven't been compiled with these safties in place, so you aren't completely safe, but if you use ZIO[5]/Typelevel[6] libraries you can be reasonably assured of referentially transparent code in practice.

There are three schools of thought, roughly, in the scala community towards the depth of using the type system and linters to provide guarantees and capabilities, currently:

1) Don't attempt to do this, it makes the barrier to entry to high for Scala juniors. I don't understand this argument - you want to allow runtime footguns you could easily prevent at compile time because the verifiable techniques take time to learn? Why did you even choose to use a typesafe language and pay the compilation time penalty that comes with it?

2) Abstract everything to the smallest possible dependency interface, including effects (code to an effect runtime, F[_] that implements the methods your code needs to run - if you handle errors, F implements MonadError, if you output do concurrent things, F implements Concurrent, etc.) and you extend the effect with your own services using tagless final or free.

3) You still use effect wrappers, but you bind the whole project always to use a concrete effect type, avoiding event abstraction, thus making it easier to code, and limiting footguns to a very particular subset (mainly threadpool providers and unsafeRun or equivalent being called eagerly in the internals of applications).

My opinion is that smallest interface with effect guarantees (#2) is best for very large, long maintenance window apps where thechoice of effect runtime might change(app), or is out of the devs' control (lib); and #3 is best for small apps.

TL/DR; You can go a really, really long way to guaranteeing effects don't run in user code in scala. Not all the way like Haskell, but far enough that it's painful to code without conforming to referential transparency.

1. https://github.com/scalacenter/scalafix

2. https://github.com/scalaz/scalazzi

3. http://www.wartremover.org/

4. https://typelevel.org/cats/api/cats/MonadError.html

5. https://zio.dev/

6. https://typelevel.org/