def strcat(s1: String)(s2: String) = s1 + s2

def strcat(s1: String) = (s2: String) => s1 + s2

strcat("foo")("bar")

object Demo {
   def main(args: Array[String]) = {
      val str1:String = "Hello, "
      val str2:String = "Scala!"

      println( "str1 + str2 = " +  strcat(str1)(str2) )
   }

   def strcat(s1: String)(s2: String) = {
      s1 + s2
   }
}

str1 + str2 = Hello, Scala!