A modern programming language that makes developers happier.

kotlinlang

Hello, I'm new to Java and Kotlin. I'm  coming from 8 years JS and PHP experience. So please bare with me. I have two questions:
1) Why is this
```
fun main() {
	println(fun (){})
}
```
giving me sunch an ungly error instead of just something like "wrong parameter type, expected string got function"?
2) how much of java should I learn to be proficient in Kotlin? I mean especially debugging tool? I assume some build/dependency tool like Gradle. How much of JVM and JVM bytecode should I understand indepth. How much of java standard library. I want to be good end efficient in Kotlin. This language looks very sexy, expressive, concise and powerful. It looks like what JavaScript should be... What it could be...