Scala "illegal start of simple expression" 定义函数时

Question

我在 Scala 上遇到以下错误：

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

// sum takes a function that takes an integer and returns an integer then
// returns a function that takes two integers and returns an integer
def sum(f: Int => Int): (Int, Int) => Int =
  def sumf(a: Int, b: Int): Int = f(a) + f(b)
  sumf

// Exiting paste mode, now interpreting.

<pastie>:4: error: illegal start of simple expression
  def sumf(a: Int, b: Int): Int = f(a) + f(b)
  ^

我不明白为什么 def 是 illegal start of simple expression。我只是想声明一个函数。我是否违反了声明中的任何语法要求？谢谢。

更新：这是我的 Scala 版本：

sbt:jaime> console
[info] Starting scala interpreter...
Welcome to Scala 2.12.10 (OpenJDK 64-Bit Server VM, Java 11.0.14).
Type in expressions for evaluation. Or try :help.

scala>

Answer 1

正如 Luis Miguel Mejía Suárez 在对此问题的评论中提到的那样，有两种方法可以使其发挥作用。

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

def sum(f: Int => Int): (Int, Int) => Int = {
  def sumf(a: Int, b: Int): Int = f(a) + f(b)
  sumf
}

// Exiting paste mode, now interpreting.

sum: (f: Int => Int)(Int, Int) => Int

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

def sum(f: Int => Int): (Int, Int) => Int = (a, b) => f(a) + f(b)

// Exiting paste mode, now interpreting.

sum: (f: Int => Int)(Int, Int) => Int

scala>

Scala "illegal start of simple expression" 定义函数时

Scala "illegal start of simple expression" when defining a function

scala