test.kt

class Human(val name: String, val age: Int, val children: List<Human>)

val age: Int? = null
    
print(::Human.curry() `$` "John" `*` age `*` listOf<Human>()) // == null
print(::Human.curry() `$` "Mary" `*` 999 `*` listOf<Human>()) // != null

util.kt

fun<A, B, Z> Function2<A, B, Z>.curry(): (A) -> (B) -> Z {
    return { a: A -> { b: B -> this(a, b) } }
}

fun<A, B, C, Z> Function3<A, B, C, Z>.curry(): (A) -> (B) -> (C) -> Z {
    return { a: A -> { b: B -> { c: C -> this(a, b, c) } } }
}

infix fun<A, B> Function1<A, B>?.`*`(a: A?): B? = this?.let { f -> a?.let(f) }
infix fun<A, B> Function1<A, B> .`$`(a: A?): B? = this `*` a