Structural function composition in Scala

compose.scala

scala> val f = (_: Int) + 1
f: Int => Int = <function1>

scala> val g = (_: Int).toString
g: Int => String = <function1>

scala> case class Compose[a,b,c](f: a => b, g: b => c) extends Function[a,c]  {
     | def apply(a: a): c = g(f(a))
     | }
defined class Compose

scala> val h = Compose(f,g)
h: Compose[Int,Int,String] = <function1>

scala> h(2)
res0: String = 3

scala> val Compose(x,y) = h
x: Int => Int = <function1>
y: Int => String = <function1>