General kotlin code syntax

fun start(): String = "Ok"

fun main() {
    val options = listOf("hello", "World")
    val output = joinOptions(options)
    println("Printing ${output}")// prints[Hello, World]
}
fun joinOptions(options: Collection<String>) = options.joinToString(prefix = "[", postfix = "]")

fun foo(name: String, number: Int = 42, toUpperCase: Boolean = false) =
        (
            if (toUpperCase)  {
            name.uppercase() }
         else  {
             name
         }
        ) + number

fun useFoo() = listOf(
        foo("a"),
        foo("b", number = 1),
        foo("c", toUpperCase = true),
        foo(name = "d", number = 2, toUpperCase = true)
)