我正在map3 // Exercise 3: The apply method is useful for implementing map3, map4, and so on
// and the pattern is straightforward. Implement map3 and map4 using only
// unit, apply, and the curried available on functions.
def map3[A,B,C,D](fa: F[A],
fb: F[B],
fc: F[C])(f: (A, B, C) => D): F[D] = {
def foo: (A => B => C => D) = (f _).curried // compile-time error
def fooF: F[A => B => C => D] = unit(foo)
val x: F[B => C => D] = apply(fooF)(fa)
val y: F[C => D] = apply(x)(fb)
val z: F[D] = apply(y)(fc)
z
}
处理[error] C:\...\Applicative.scala: _ must follow method; cannot follow f.type
[error] def foo: (A => B => C => D) = (f _).curried
[error]
^
。
curried上面提到的一行发生了一（1）次编译时错误：
{{1}}
我通过这篇文章成功获得了{{1}}版本的功能 - Functional Programming in Scala。
但是，我不明白上面的编译时错误。
答案 0 :(得分：6)
错误是因为f这里是一个函数，而不是一个方法; f _语法是将方法转换为函数，这在此不是必需的。只需写下def foo: A => B => C => D = f.curried。