gistfile1.scala

scala> def f[A](x: A, xs: List[A]): List[A] = x :: xs
f: [A](x: A, xs: List[A])List[A]

scala> def g[A](x: A)(xs: List[A]): List[A] = x :: xs
g: [A](x: A)(xs: List[A])List[A]

scala> f(3, _)
<console>:9: error: missing parameter type for expanded function ((x$1) => f(3, x$1))
    f(3, _)
         ^

scala> f(3, _: List[Int])
res1: List[Int] => List[Int] = <function1>

scala> g(3) _
res2: List[Int] => List[Int] = <function1>