U+25B6 BLACK RIGHT-POINTING TRIANGLE: ▶ U+25B8 BLACK RIGHT-POINTING SMALL TRIANGLE: ▸ U+25BC BLACK DOWN-POINTING TRIANGLE: ▼ U+25BE BLACK DOWN-POINTING SMALL TRIANGLE: ▾ https://en.wikipedia.org/wiki/Geometric_Shapes_(Unicode_block)#U+25A0-U+25CF More on reddit.com

Without seeing it, other IDEs have very similar things -- you're able to click on it and just collapse the HTML element in your view -- for instance, if you have a 20-line that you want to hide, you can click that arrow and minimize it from view. It doesn't change the code itself. More on reddit.com

I’m new to Kotlin so take this with a grain of salt. I’m migrating some of our Java backend to Kotlin and using Arrow in the refactoring. This is primarily for error handling with Either but I’ve found places to make use of ArrowFx and Optics as well for one particular deeply nested domain model. Arrow is still an evolving library and I see some complaints in this thread that since Kotlin doesn’t embrace FP in the same way that Scala or Haskell do that Arrow is crippled in providing FP primitives. I had the same questions recently in a thread on this sub. At the very least I know that Arrow helps me write more concise/declarative code than if I didn’t have it and I can’t say the same thing for something like Vavr in Java. At the end of the day, most of my job is writing JVM based Lambdas and Kotlin + Arrow seems like my path of least resistance. I want to add: Arrow is taking a very opinionated stance by limiting itself to what works well with the standard library. It’s not a complete FP toolbox. In doing so they require just using coroutines to model and compose effects and are putting a lot of eggs in the context receivers basket. I’m not sure how those choices will play out long term. More on reddit.com

You aren't linking the arrow library, so the linker can't find any of the function definitions. You need to tell the linker what libraries you want with -l. So without being able to test myself I'd suggest using -larrow. More on reddit.com