since there are no checked exceptions in kotlin, is it best to have error return values instead?

You still have exceptions that you can catch... they are just not checked. But, if you like function-style programming, making your functions more pure by either carrying a good return value or an error value (e.g.

Either<E,T>

), that'd be better than them throwing an exception...

Imo, exceptions should be exceptional. If your code needs to halt and catch fire when something genuinely unexpected happens, use an exception. If it's expected to happen sometimes, use either a nullable return or a sealed class return if you want more detailed information

makes sense. remind me of programming in c having result codes everywhere

This can help to make a decision https://kotlinlang.slack.com/archives/C0922A726/p1536388784000100?thread_ts=1536360062.000100&cid=C0922A726

Nothing prevents you to catch exception, they’re just not enforced by the compiler, unlike Java. On a functional side, adding to the excellent advice above, you could use

Result

from standard lib (https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-result/index.html) or

Either

if using Arrow (https://arrow-kt.io/docs/arrow/core/either/#either)