（Protocol.UndefinedError）协议枚举未实现3 [英] (Protocol.UndefinedError) protocol Enumerable not implemented for 3

问题描述

我想在理解之后返回总计金额。这是我正在尝试的：

I'm trying to return a summed amount after a comprehension. Here is what I'm trying:

range = 1..999

multiple_of_3_or_5? = fn(n) -> (rem(n, 3) == 0 || rem(n, 5) == 0) end
for n <- range, multiple_of_3_or_5?.(n),
  do: Enum.reduce(n, 0, fn(x, y) -> (x + y) end)

<这似乎应该总结从理解中返回的列表，而是打印此错误：

This seems like it should sum the list that is returned from the comprehension but instead it prints this error:

#=> ** (Protocol.UndefinedError) protocol Enumerable not implemented for 3

任何人都可以帮助这个？ p>

Can anyone help with this?

推荐答案

你正在传递每个整数，而不是过滤的列表。您应将的结果传递给 Enum.reduce / 3 ：

You're passing each integer to reduce instead of the filtered list. You should pass the result of the for to Enum.reduce/3:

iex(1)> range = 1..999
1..999
iex(2)> multiple_of_3_or_5? = fn(n) -> (rem(n, 3) == 0 || rem(n, 5) == 0) end
#Function<6.118419387/1 in :erl_eval.expr/5>
iex(3)> for(n <- range, multiple_of_3_or_5?.(n), do: n) |> Enum.reduce(0, fn(x, y) -> (x + y) end)
233168

您还可以使用 Enum.sum / 1 来缩短这一点：

You can also use Enum.sum/1 to shorten this:

iex(4)> Enum.sum for n <- range, multiple_of_3_or_5?.(n), do: n
233168

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