Partially applied functions with selective arg application

PartiallyAppliedFn.kt

package arrow.core

public fun interface Partial<A, B, C, D, Z> {
  public operator fun invoke(a: A, b: B, c: C, d: D): Z

  public fun first(a: A): Partial<Unit, B, C, D, Z> =
    Partial { _, b, c, d -> invoke(a, b, c, d) }

  public fun second(b: B): Partial<A, Unit, C, D, Z> =
    Partial { a, _, c, d -> invoke(a, b, c, d) }

  public fun third(c: C): Partial<A, B, Unit, D, Z> =
    Partial { a, b, _, d -> invoke(a, b, c, d) }

  public fun fourth(d: D): Partial<A, B, C, Unit, Z> =
    Partial { a, b, c, _ -> invoke(a, b, c, d) }

  public companion object {
    public operator fun <A, B, C, D, Z> invoke(f: (A, B, C, D) -> Z): Partial<A, B, C, D, Z> =
      Partial { a, b, c, d -> f(a, b, c, d) }

    public operator fun <A, B, C, Z> invoke(f: (A, B, C) -> Z): Partial<A, B, C, Unit, Z> =
      Partial { a, b, c, _ -> f(a, b, c) }

    public operator fun <A, B, Z> invoke(f: (A, B) -> Z): Partial<A, B, Unit, Unit, Z> =
      Partial { a, b, _, _ -> f(a, b) }

    public operator fun <A, Z> invoke(f: (A) -> Z): Partial<A, Unit, Unit, Unit, Z> =
      Partial { a, _, _, _ -> f(a) }
  }
}

@JvmName("apply1")
public operator fun <A, Z> Partial<A, Unit, Unit, Unit, Z>.invoke(first: A): Z =
  invoke(first, Unit, Unit, Unit)

public operator fun <B, Z> Partial<Unit, B, Unit, Unit, Z>.invoke(second: B): Z =
  invoke(Unit, second, Unit, Unit)

public fun divide(num: Int, den: Int): Int =
  num / den

public data class User(val id: Int, val name: String)

public fun createUser(name: String, id: Int): User =
  User(id, name)

public fun main() {
  val halfOf = Partial(::divide).second(2)
  val ten: Int = halfOf(20)

  val createUserJaneWithId = Partial(::createUser).first("Jane")
  val jane = createUserJaneWithId(ten)
  println(jane) //User(id=10, name=Jane)
}