Elixir - 調用/調用宏 - UndefinedFunctionError

Question

為什么靈葯報告UndefinedFunctionError調用使用宏時Module.macroName語法在.exs文件？ 我似乎只能調用宏，如果我有另一個調用宏的函數，我調用函數而不是宏。

下面的代碼演示了這個

defmodule Sample do
  defmacro doIt(expression) do
    quote do
      IO.puts unquote(expression)
    end
  end

  def doFunc(e), do: doIt(e)
end

Sample.doFunc "Hello World via Function" # Works fine
Sample.doIt "Hello World from Macro!" # Gives error

產量

Hello World via Function
** (UndefinedFunctionError) undefined function: Sample.doIt/1
    Sample.doIt("Hello World from Macro!")
    (elixir) lib/code.ex:307: Code.require_file/2

Elixir文檔示例使用iex ，而不是在.exs文件中調用宏。 即使是上面的代碼，如果我們刪除對Sample.doIt調用並將其加載到iex ，然后調用Sample.doIt工作正常。

E:\elixir>iex hello.exs
Hello World via Function
Interactive Elixir (1.0.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> require Sample
nil
iex(2)> Sample.doIt "Hello"
Hello
:ok
iex(3)>

如果我嘗試在上面的文件中require Sample ，如下所示

defmodule Sample
  ... rest of stuff as shown above ...
end

require Sample

Sample.doFunc "Hello World via Function"
Sample.doIt "Hello World from Macro!"

我收到錯誤

** (CompileError) hello.exs:11: module Sample is not loaded but was defined. This happens because you are trying to use a module in the same context it is defined. Try defining the module outside the context that requires it.
    (stdlib) lists.erl:1352: :lists.mapfoldl/3
    (stdlib) lists.erl:1353: :lists.mapfoldl/3

Answer 1

像往常一樣，在使用宏之前需要一個模塊來向編譯器表明編譯模塊的順序：

defmodule Other do
  def run do
    require Sample

    Sample.doFunc "Hello World via Function"
    Sample.doIt "Hello World from Macro!"
  end
end

Other.run # => Hello World via Function
          #    Hello World from Macro!