Type Matching in Scala

tmatch.scala

scala> :paste
// Entering paste mode (ctrl-D to finish)

val fn = tmatch(
  when[Int] { i => i + 1 }
  when[String] { s => s.toInt }
  when[Symbol] { s => 3.1415926 }
  when[Double] { d => "You entered a double" }
)

// Exiting paste mode, now interpreting.

fn: typematch.tmatch[Double,Symbol,String,Int,Nothing,Nothing,Nothing,String,Double,Int,Int,Nothing,Nothing,Nothing,Nothing] = tmatch(Cons(<function1>,Cons(<function1>,Cons(<function1>,Cons(<function1>,null)))))

scala> fn(1)
res0: Int = 2

scala> fn("3")
res1: Int = 3

scala> fn('pi)
res2: Double = 3.1415926

scala> fn(4.0)
res3: String = You entered a double

scala> fn(true)
<console>:15: error: could not find implicit value for parameter m: fn.Stack[Boolean]
       fn(true)
         ^