There are a couple of typos and unclarities in exercise 4.x:

4.3:

the text shows that the expected output of the following code should be *abc:

val starPrefixFn = ::strConcat.curry()("*") println(starPrefixFn("abc")) 

However, the strConcat is defined with a space so the expected output should be * abc

in 4.4 the class EmailTemplate inherits from a function so we can use the invoke() function, but it should be written with the override keyword as follow:

class EmailTemplate(fileName: String): (Person) -> String { override fun invoke(aPerson: Person): String = TODO() }