In Scala, we can partially apply arguments to return new functions.

scala> def add(x: Int)(y: Int) = x + y
add: (Int)(Int)Int

scala> def foo = add(7) _
foo: (Int) => Int

scala> val h = foo(8)
h: Int = 15            
          

We can get very funky indeed.

scala> val i = List(1, 2, 3) map foo
i: List[Int] = List(8, 9, 10)
          

Our encoder.

scala> def encoder: String => String => Array[Byte] = null // todo
encoder: (String) => (String) => Array[Byte]
            
scala> def utf8 = encoder("UTF-8")
utf8: (String) => Array[Byte]

scala> def encoded = utf8("contents")
encoded: Array[Byte]