此Elixir表达式的正确语法是什么? [英] What is the correct syntax for this Elixir expression?

问题描述

已向我提供了此代码段，作者尚未对其进行测试，

I have been proferred this code snippet, which the author has not tested,

|> (fn l ->[?[, Enum.map(l, &([inspect(limit: :infinity), ?\n])), ?]] end).()

作为管道命令序列的一部分，该命令使用 DataMorph将数据从CSV文件转换为struct 库，并将结果作为常规的Elixir列表输出，以输入到Elixir源中-即添加括号，并用逗号分隔列表中的元素.

as part of a sequence of pipelined commands which converts data from a CSV file to a struct using the DataMorph library, and outputs the result as a regular Elixir list for input into Elixir source - ie adding the surrounding brackets, and separating the elements of the list with commas.

以下是该序列的含义:

File.stream!('tmp.csv') \
|> DataMorph.structs_from_csv("open-register", :iso_country) \
|> (fn l ->[?[, Enum.map(l, &([inspect(limit: :infinity), ?\n])), ?]] end).()
|> (&File.write('output.txt',&1)).()

这是在iex中运行时的错误消息:

This is the error message when it is run in iex:

* (CompileError) iex:55: invalid args for &, expected an expression in the format of &Mod.fun/arity, &local/arity or a capture containing at least one argument as &1, got: [inspect(limit: :infinity), 10]
    (elixir) expanding macro: Kernel.|>/2
             iex:55: (file)

代码段哪里出问题了?

推荐答案

可以通过将&1作为部分应用程序语法的第一个参数添加来修复语法错误:

The syntax error can be fixed by adding &1 as the first argument to the partial application syntax:

|> (fn l ->[?[, Enum.map(l, &([inspect(&1, limit: :infinity), ?\n])), ?]] end).()

此代码不包含逗号.为此，如果您想继续制作iolist，我建议您使用Enum.intersperse:

This code doesn't include a separating comma. For that, if you want to stay with producing an iolist, I'd recommend using Enum.intersperse:

iex(1)> [1, 2, [3], [4, 5]] |> (fn l ->[?[, Enum.map(l, &inspect(&1, limit: :infinity)) |> Enum.intersperse(",\n"), ?]] end).() |> IO.puts
[1,
2,
[3],
[4, 5]]

为了可读性，我还将其分成多行:

I'd also break this into multiple lines for readability:

[1, 2, [3], [4, 5]]
|> (fn list ->
  elements = Enum.map(list, &inspect(&1, limit: :infinity)) |> Enum.intersperse(",\n")
  [?[, elements, ?]]
end).()
|> IO.puts

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